PPDataContext db = new PPDataContext();

    db.ObjectTrackingEnabled = false;

    var eventTypes = from et in db.PP_Event_Types
                     orderby et.SORT_ORDER, et.TITLE
                     select new { eventType = et.EVENT_TYPE, title = et.TITLE };

    ddlProposalTypes.DataSource = eventTypes;
    ddlProposalTypes.DataValueField = "eventType";
    ddlProposalTypes.DataTextField = "title";
    ddlProposalTypes.DataBind();

    ListItem liBlank = new ListItem();
    liBlank.Value = "All";
    liBlank.Text = "All";

    ddlProposalTypes.Items.Add(liBlank);
    ddlProposalTypes.SelectedValue = "All";

Error: ddlProposalTypes' has a SelectedValue which is invalid because it does not exist in the list of items. 

 I get this error at this line:  ddlProposalTypes.DataBind();

I don't get any error the first time i go to this page, but after first time it's hit and miss.

 I am not even setting the selectedValues until later in the code.

Any help is much appriciated!

irbanjit:

 

    PPDataContext db = new PPDataContext();

    db.ObjectTrackingEnabled = false;

    var eventTypes = from et in db.PP_Event_Types
                     orderby et.SORT_ORDER, et.TITLE
                     select new { eventType = et.EVENT_TYPE, title = et.TITLE };

    ddlProposalTypes.DataSource = eventTypes;
    ddlProposalTypes.DataValueField = "eventType";
    ddlProposalTypes.DataTextField = "title";
    ddlProposalTypes.DataBind();

    ListItem liBlank = new ListItem();
    liBlank.Value = "All";
    liBlank.Text = "All";

    ddlProposalTypes.Items.Add(liBlank);
    ddlProposalTypes.SelectedValue = "All";

Error: ddlProposalTypes' has a SelectedValue which is invalid because it does not exist in the list of items. 

 I get this error at this line:  ddlProposalTypes.DataBind();

I don't get any error the first time i go to this page, but after first time it's hit and miss.

 I am not even setting the selectedValues until later in the code.

Any help is much appriciated!

Hi irbanjit,

After test, your code works.

So I think maybe your code likes following code, if so, please remove if(!IsPostBack), refer the following code:
 

    if (!IsPostBack)
        {
            DataClassesDataContext dcdc = new DataClassesDataContext();
            var eventTypes = from c in dcdc.Products
                             select new { ID1 = c.CategoryID, ID2 = c.ProductID };
            this.DropDownList1.DataSource = eventTypes;
            this.DropDownList1.DataTextField = "ID1";
            this.DropDownList1.DataValueField = "ID2";
            this.DropDownList1.DataBind();
        }

Hope it helps,

Hong Gang