fkToOrgID is an integer used to select records based on a company ID field (pretty basic stuff ). There is no C# code at the moment as I am just familiarising myself with ASP.net and trying to keep it simple (maybe that is my problem!). I have a drop down list (ddlTradPartyTo) which is the source of this parameter. If I run the query with no parameters (so return results for all copanies) it works 100% fine - paging, sorting no problem. Only when I introduce parameters does this problem occur! The code compiles fine, but when launched produces the error below.

The ASP code for my ObjectDataSource:
<asp:ObjectDataSource ID="ODS" runat="server" OldValuesParameterFormatString="original_{0}" SelectMethod="GetPageTransactions" TypeName="BLL"EnablePaging="True" SelectCountMethod="GetTransactionCount" SortParameterName="sortExpression">
<SelectParameters>
<asp:ControlParameter ControlID="ddlTradPartyTo" Name="fkToOrgID" PropertyName="SelectedValue" Type="string" DefaultValue="0" />
</SelectParameters>
</asp:ObjectDataSource>

The ASP code for my GridView:
<%--Gridview--%>
<asp:GridView ID="GridView1" runat="server" AllowPaging="True" AllowSorting="True" AutoGenerateColumns="False" CellPadding="4" DataSourceID="ODS" ForeColor="#333333" GridLines="None" DataKeyNames="pkTransactionID">
<FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
<RowStyle BackColor="#EFF3FB" />
<EditRowStyle BackColor="#2461BF" />
<SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
<PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
<HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
<AlternatingRowStyle BackColor="White" />
<Columns>
<asp:BoundField DataField="pkTransactionID" HeaderText="pkTransactionID" InsertVisible="False"
ReadOnly="True" SortExpression="pkTransactionID" />
<asp:BoundField DataField="fkDocClassCD" HeaderText="fkDocClassCD" SortExpression="fkDocClassCD" />
<asp:BoundField DataField="fkFromOrgID" HeaderText="fkFromOrgID" SortExpression="fkFromOrgID" />
<asp:BoundField DataField="fkToOrgID" HeaderText="fkToOrgID" SortExpression="fkToOrgID" />
<asp:BoundField DataField="fkErrorCode" HeaderText="fkErrorCode" SortExpression="fkErrorCode" />
<asp:BoundField DataField="fkStatus" HeaderText="fkStatus" SortExpression="fkStatus" />
<asp:BoundField DataField="DateTimeReceived" HeaderText="DateTimeReceived" SortExpression="DateTimeReceived" />
<asp:BoundField DataField="DateTimeSent" HeaderText="DateTimeSent" SortExpression="DateTimeSent" />
<asp:BoundField DataField="NetFileSize" HeaderText="NetFileSize" SortExpression="NetFileSize" />
</Columns>
</asp:GridView>

The ASP code for my DataSource (for the GridView):
<asp:SqlDataSource ID="sqlOrganisations" runat="server" ConnectionString="<%$ ConnectionStrings:RobConnectionString %>"
SelectCommand="SELECT [pkOrganisationID], [OrganisationName] FROM [CO_Organisation] ORDER BY [OrganisationName]">
</asp:SqlDataSource>

The error that is generated is :

Line 29:     public int GetTransactionCount(int fkToOrgID)
Line 30:     {
Line 31:         return (int)Adapter.usp_GetTransactionCount(fkToOrgID);
Line 32:     }
Line 33: 

[NullReferenceException: Object reference not set to an instance of an object.]
   BLL.GetTransactionCount(Int32 fkToOrgID) in c:\Dev\Training\GridViewPrac\App_Code\BLL\BLL.cs:31

[TargetInvocationException: Exception has been thrown by the target of an invocation.]
   System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) +0
   System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) +72
   System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) +358
   System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) +29
   System.Web.UI.WebControls.ObjectDataSourceView.InvokeMethod(ObjectDataSourceMethod method, Boolean disposeInstance, Object& instance) +482
   System.Web.UI.WebControls.ObjectDataSourceView.QueryTotalRowCount(IOrderedDictionary mergedParameters, DataSourceSelectArguments arguments, Boolean disposeInstance, Object& instance) +254
   System.Web.UI.WebControls.ObjectDataSourceView.ExecuteSelect(DataSourceSelectArguments arguments) +2186
   System.Web.UI.DataSourceView.Select(DataSourceSelectArguments arguments, DataSourceViewSelectCallback callback) +17
   System.Web.UI.WebControls.DataBoundControl.PerformSelect() +149
   System.Web.UI.WebControls.BaseDataBoundControl.DataBind() +70
   System.Web.UI.WebControls.GridView.DataBind() +4
   System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound() +82
   System.Web.UI.WebControls.CompositeDataBoundControl.CreateChildControls() +69
   System.Web.UI.Control.EnsureChildControls() +87
   System.Web.UI.Control.PreRenderRecursiveInternal() +41
   System.Web.UI.Control.PreRenderRecursiveInternal() +161
   System.Web.UI.Control.PreRenderRecursiveInternal() +161
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1360