I added your code to the page _load event and it still isn't working. Here is the entire code behind page, just so you can see how I have it On page A: Also Should all of the code go in the code behind on Page A or am I supposed to put it in the page_load event for page B:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Web.UI.WebControls;
using NPOI.HSSF.UserModel;
using NPOI.HSSF.Util;
using NPOI.SS.UserModel;
using Telerik.Web.UI;
using System.Data;
using System.Web.UI;

public partial class AdvancedSearch : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["selection"] != null)
        {
            // Get your selected items
            var selectedItems = Session["selection"] as List<string>;

            foreach (ListItem listItem in Equipment_Fields.Items)
            {
                // Select this item if it is present
                listItem.Selected = selectedItems.Contains(listItem.Value);
            }
        }


        if (!IsPostBack)
        {
            Master.SelItem = "Advanced Search";
            Master.SetTitle("Advanced Search");

            Results.Visible = true;
        }


    }
    protected void Submit_Click(object sender, EventArgs e)
    {
        List<string> selections = new List<string>();
        foreach (ListItem listItem in Equipment_Fields.Items)
        {
            if (listItem.Selected)
            {
                selections.Add(listItem.Value);
            }
        }

        Session["selections"] = selections;

       

        string searchValue = SearchValue.Text.Trim();
        string errorMessage = string.Empty;
        Results.Visible = false;

        bool searchEquipment = GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Fields) + GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Type) + GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Status) > 0;
        bool searchHistory = GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(History_Fields) + GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(History_Status) > 0;
        bool searchOTR = GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(OTR_Fields) + GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(OTR_Classification) > 0;

        if (searchEquipment == false && searchHistory == false && searchOTR == false)
        {
            errorMessage += "There's no field to be searched selected.<br/>";
        }
        if (searchEquipment)
        {
            if (GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Type) == 0)
            {
                errorMessage += "There's no <strong>Equipment Type</strong> to be searched selected.<br/>";
            }
            if (GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Status) == 0)
            {
                errorMessage += "There's no <strong>Equipment Status</strong> to be searched selected.<br/>";
            }
        }
        if (searchHistory)
        {
            if (GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(History_Status) == 0)
            {
                errorMessage += "There's no <strong>History Status</strong> to be searched selected.<br/>";
            }
        }
        if (searchOTR)
        {
            if (GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(OTR_Classification) == 0)
            {
                errorMessage += "There's no <strong>OTR Classification</strong> to be searched selected.<br/>";
            }
        }

        if (!string.IsNullOrEmpty(errorMessage))
        {
            GiTools.Telerik.RadWindow.RadError(Master.WindowManager_Error, errorMessage);

            ShowHideSearchOptions.Text = "Hide Search Options";
            Search_Options_Container.Style.Add("display", "");
        }
        else
        {
            Results.Visible = true;
            Results.Rebind();

            ShowHideSearchOptions.Text = "Show Search Options";
            Search_Options_Container.Style.Add("display", "none");
        }

        if (Filter_By_Date.Checked)
        {
            Date_Start.Enabled = Date_End.Enabled = true;
        }
        else
        {
            Date_Start.Enabled = Date_End.Enabled = false;
        }
    }

    private string GetSearchQuery()
    {
        string searchValue = SearchValue.Text.Trim();
        StringBuilder queryString = new StringBuilder();
        bool searchEquipment = GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Fields) + GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Type) + GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Status) > 0;
        bool searchHistory = GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(History_Fields) + GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(History_Status) > 0;
        bool searchOTR = GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(OTR_Fields) + GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(OTR_Classification) > 0;

        if (searchEquipment)
        {
            queryString.Append("SELECT equipment.equipment_id, equipment.equipment_id AS id, CAST(equipment.tms_num as varchar(30)) AS id_label, LEN(equipment.tms_num) AS id_label_length, 'Equipment' AS type, equipment.description AS description FROM equipment WHERE 1=1");

            if (!string.IsNullOrEmpty(searchValue) && GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Fields) > 0)
            {
                StringBuilder whereClause = new StringBuilder(" AND (1=2");
                if (Equipment_Fields.Items.FindByValue("TMS #").Selected) whereClause.Append(string.Format(" OR equipment.tms_num LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Assigned To").Selected) whereClause.Append(string.Format(" OR equipment.assigned_to LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Issued To").Selected) whereClause.Append(string.Format(" OR equipment.issued_to LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Department").Selected) whereClause.Append(string.Format(" OR equipment.department LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Manufacturer").Selected) whereClause.Append(string.Format(" OR equipment.manufacturer LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Model #").Selected) whereClause.Append(string.Format(" OR equipment.model_num LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Serial #").Selected) whereClause.Append(string.Format(" OR equipment.serial_num LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Description").Selected) whereClause.Append(string.Format(" OR equipment.description LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Characteristics").Selected) whereClause.Append(string.Format(" OR equipment.characteristics LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Calibration Procedure").Selected) whereClause.Append(string.Format(" OR equipment.calibration_procedure LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Calibration Standard").Selected) whereClause.Append(string.Format(" OR equipment.calibration_standard LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Calibration Interval").Selected) whereClause.Append(string.Format(" OR equipment.calibration_interval LIKE '{0}'", searchValue));
                if (Equipment_Fields.Items.FindByValue("Required Accuracy").Selected) whereClause.Append(string.Format(" OR equipment.required_accuracy LIKE '{0}'", searchValue));
                whereClause.Append(")");
                queryString.Append(whereClause.ToString());
            }

            if (GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Type) == 1)
            {
                queryString.Append(string.Format(" AND equipment.type = {0}", Equipment_Type.SelectedValue));
            }
            if (GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(Equipment_Status) < Equipment_Status.Items.Count)
            {
                queryString.Append(string.Format(" AND equipment.status IN ({0})", string.Join(",", GiTools.UI.Controls.CheckBoxList.GetCheckedItemsValues(Equipment_Status).ToArray())));
            }
            if (!Equipment_Status_Obsolete.Items.FindByValue("Include Obsolete").Selected)
            {
                queryString.Append(" AND equipment.is_obsolete = 0");
            }

            if (Filter_By_Date.Checked)
            {
                if (Date_Start.SelectedDate.HasValue)
                {
                    queryString.Append(" AND equipment.date_submitted >= '" + Date_Start.SelectedDate.Value.Date + "'");
                }
                if (Date_End.SelectedDate.HasValue)
                {
                    queryString.Append(" AND equipment.date_submitted <= '" + Date_End.SelectedDate.Value.Date.AddDays(1).AddMilliseconds(-1) + "'");
                }
                if (Date_Start.SelectedDate.HasValue)
                {
                    queryString.Append(" AND equipment.date_submitted >= '" + Date_Start.SelectedDate.Value.Date + "'");
                }
                if (Date_End.SelectedDate.HasValue)
                {
                    queryString.Append(" AND equipment.date_submitted <= '" + Date_End.SelectedDate.Value.Date.AddDays(1).AddMilliseconds(-1) + "'");
                }
            }
        }

        if (searchHistory)
        {
            if (queryString.Length > 0)
            {
                queryString.Append(" UNION ALL ");
            }
            queryString.Append("SELECT equipment.equipment_id, history_id AS id, CAST(history_id as varchar(30)) AS id_label, LEN(history_id) AS id_label_length, 'History' AS type, 'TMS # ' + equipment.tms_num + ': ' + history.remarks AS description FROM history INNER JOIN equipment ON history.equipment_id = equipment.equipment_id WHERE 1=1");

            if (!string.IsNullOrEmpty(searchValue) && GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(History_Fields) > 0)
            {
                StringBuilder whereClause = new StringBuilder(" AND (1=2");
                if (History_Fields.Items.FindByValue("ID Number").Selected) whereClause.Append(string.Format(" OR history.history_id LIKE '{0}'", searchValue));
                if (History_Fields.Items.FindByValue("Inspector").Selected) whereClause.Append(string.Format(" OR history.inspector LIKE '{0}'", searchValue));
                if (History_Fields.Items.FindByValue("Inspector E-mail").Selected) whereClause.Append(string.Format(" OR history.inspector_email LIKE '{0}'", searchValue));
                if (History_Fields.Items.FindByValue("Remarks").Selected) whereClause.Append(string.Format(" OR history.remarks LIKE '{0}'", searchValue));
                whereClause.Append(")");
                queryString.Append(whereClause.ToString());
            }

            if (GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(History_Status) < History_Status.Items.Count)
            {
                queryString.Append(string.Format(" AND history.status IN ({0})", string.Join(",", GiTools.UI.Controls.CheckBoxList.GetCheckedItemsValues(History_Status).ToArray())));
            }

            if (Filter_By_Date.Checked)
            {
                if (Date_Start.SelectedDate.HasValue)
                {
                    queryString.Append(" AND history.date_submitted >= '" + Date_Start.SelectedDate.Value.Date + "'");
                }
                if (Date_End.SelectedDate.HasValue)
                {
                    queryString.Append(" AND history.date_submitted <= '" + Date_End.SelectedDate.Value.Date.AddDays(1).AddMilliseconds(-1) + "'");
                }
                if (Date_Start.SelectedDate.HasValue)
                {
                    queryString.Append(" AND history.date_submitted >= '" + Date_Start.SelectedDate.Value.Date + "'");
                }
                if (Date_End.SelectedDate.HasValue)
                {
                    queryString.Append(" AND history.date_submitted <= '" + Date_End.SelectedDate.Value.Date.AddDays(1).AddMilliseconds(-1) + "'");
                }
            }
        }

        if (searchOTR)
        {
            if (queryString.Length > 0)
            {
                queryString.Append(" UNION ALL ");
            }
            queryString.Append("SELECT equipment.equipment_id, otr_id AS id, CAST(otr_id as varchar(30)) AS id_label, LEN(otr_id) AS id_label_length, 'OTR' AS type, 'TMS # ' + equipment.tms_num + ': ' + otr.submitter_comments AS description FROM otr INNER JOIN equipment ON otr.equipment_id = equipment.equipment_id WHERE 1=1");

            if (!string.IsNullOrEmpty(searchValue) && GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(OTR_Fields) > 0)
            {
                StringBuilder whereClause = new StringBuilder(" AND (1=2");
                if (OTR_Fields.Items.FindByValue("ID Number").Selected) whereClause.Append(string.Format(" OR otr.otr_id LIKE '{0}'", searchValue));
                if (OTR_Fields.Items.FindByValue("Submitter").Selected) whereClause.Append(string.Format(" OR otr.submitted_by LIKE '{0}'", searchValue));
                if (OTR_Fields.Items.FindByValue("Submitter E-mail").Selected) whereClause.Append(string.Format(" OR otr.submitted_by_email LIKE '{0}'", searchValue));
                if (OTR_Fields.Items.FindByValue("Actual accuracy").Selected) whereClause.Append(string.Format(" OR otr.actual_accuracy LIKE '{0}'", searchValue));
                whereClause.Append(")");
                queryString.Append(whereClause.ToString());
            }

            if (searchOTR && GiTools.UI.Controls.CheckBoxList.GetCheckedItemsCount(OTR_Classification) == 1)
            {
                queryString.Append(string.Format(" AND otr.classification = {0}", OTR_Classification.SelectedValue));
            }

            if (Filter_By_Date.Checked)
            {
                if (Date_Start.SelectedDate.HasValue)
                {
                    queryString.Append(" AND otr.date_submitted >= '" + Date_Start.SelectedDate.Value.Date + "'");
                }
                if (Date_End.SelectedDate.HasValue)
                {
                    queryString.Append(" AND otr.date_submitted <= '" + Date_End.SelectedDate.Value.Date.AddDays(1).AddMilliseconds(-1) + "'");
                }
                if (Date_Start.SelectedDate.HasValue)
                {
                    queryString.Append(" AND otr.date_submitted >= '" + Date_Start.SelectedDate.Value.Date + "'");
                }
                if (Date_End.SelectedDate.HasValue)
                {
                    queryString.Append(" AND otr.date_submitted <= '" + Date_End.SelectedDate.Value.Date.AddDays(1).AddMilliseconds(-1) + "'");
                }
            }
        }

        queryString.Append(" ORDER BY type, id_label_length, id_label");

        return queryString.ToString();
    }

    protected void Results_NeedDataSource(object sender, GridNeedDataSourceEventArgs e)
    {
        Results.DataSource = GiTools.Database.MsSql.SqlToDataTable(Common.ConnectionString, GetSearchQuery());
    }

    protected void Results_ItemDataBound(object sender, GridItemEventArgs e)
    {
        if (e.Item is GridPagerItem)
        {
            GridPagerItem pager = (GridPagerItem)e.Item;
            Label lbl = (Label)pager.FindControl("ChangePageSizeLabel");
            lbl.Visible = false;

            RadComboBox combo = (RadComboBox)pager.FindControl("PageSizeComboBox");
            combo.Visible = false;
        }
        if (e.Item is GridDataItem)
        {
            string type = DataBinder.Eval(e.Item.DataItem, "type", string.Empty);

            if (type == "OTR")
            {
                e.Item.Cells[2].Text = string.Format("<a href='OtrView.aspx?id={0}'>{0}</a>", DataBinder.Eval(e.Item.DataItem, "id", string.Empty));
            }
            else if (type == "History")
            {
                e.Item.Cells[2].Text = string.Format("<a href='EquipmentView.aspx?id={0}'>{1}</a>", DataBinder.Eval(e.Item.DataItem, "equipment_id", string.Empty), DataBinder.Eval(e.Item.DataItem, "id", string.Empty));
            }
            else if (type == "Equipment")
            {
                e.Item.Cells[2].Text = string.Format("<a href='EquipmentView.aspx?id={0}'>{1}</a>", DataBinder.Eval(e.Item.DataItem, "equipment_id", string.Empty), DataBinder.Eval(e.Item.DataItem, "id_label", string.Empty));
            }
        }
    }

    protected void DataDump_Click(object sender, EventArgs e)
    {
        DataClassesDataContext dc = new DataClassesDataContext();
        DataTable dt = GiTools.Database.MsSql.SqlToDataTable(Common.ConnectionString, GetSearchQuery());

        HSSFWorkbook hssfworkbook = new HSSFWorkbook();
        HSSFSheet sheet = (HSSFSheet)hssfworkbook.CreateSheet("Sheet1");

        int rowIndex = 0;
        int columnIndex = 0;

        #region add table headers

        HSSFFont boldFont = (HSSFFont)hssfworkbook.CreateFont();
        boldFont.Color = HSSFColor.BLACK.index;
        boldFont.Boldweight = (short)FontBoldWeight.BOLD;

        HSSFCellStyle header_Bold = (HSSFCellStyle)hssfworkbook.CreateCellStyle();
        header_Bold.SetFont(boldFont);

        HSSFRow dataRow = (HSSFRow)sheet.CreateRow(rowIndex);

        dataRow.CreateCell(columnIndex++).SetCellValue("ID #");
        dataRow.CreateCell(columnIndex++).SetCellValue("Type");
        dataRow.CreateCell(columnIndex++).SetCellValue("Description");

        for (int i = 0; i < sheet.GetRow(0).LastCellNum; i++)
        {
            HSSFCell cell = (HSSFCell)sheet.GetRow(0).GetCell(i);
            cell.CellStyle = header_Bold;
        }

        #endregion

        #region add data

        foreach (DataRow row in dt.Rows)
        {
            rowIndex++;
            columnIndex = 0;
            dataRow = (HSSFRow)sheet.CreateRow(rowIndex);

            dataRow.CreateCell(columnIndex++).SetCellValue(GiTools.DataTypes.String.TryParse(row[1]));
            dataRow.CreateCell(columnIndex++).SetCellValue(GiTools.DataTypes.String.TryParse(row[2]));
            dataRow.CreateCell(columnIndex++).SetCellValue(GiTools.DataTypes.String.TryParse(row[3]));
        }

        #endregion

        // autosize all columns
        for (int i = 0; i < sheet.GetRow(0).LastCellNum; i++)
        {
            if (i != 12 && i != 23)
            {
                sheet.AutoSizeColumn(i);
            }
        }

        //Write the stream data of workbook to the root directory
        string fileName = "~/Downloads/Advanced-Search-Result.xls";
        FileStream file = new FileStream(Server.MapPath(fileName), FileMode.Create);
        hssfworkbook.Write(file);
        file.Close();

        GiTools.UI.Page.DownloadFile(this, fileName, true);
    }
}