Error on postback: Specified argument was out of the range of valid values.

[Dave]

I am receiving an exception whenever i peform any postback on a page with a grid.
I am adding the grid's column in code and also putting the whole grid into edit mode. The datasource is a datatable. I've been using the examples from the tutorials to get started. I also have 2 linkbuttons in the CommandItemTemplate. Whenever i click on either button, i never back it to the ItemCommand, instead i receive an exception:
DotNetNuke.Services.Exceptions.PageLoadException: Specified argument was out of the range of valid values. Parameter name: index ---> System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values. Parameter name: indexat System.Web.UI.ControlCollection.get_Item(Int32 index)at Telerik.Web.UI.GridTextBoxColumnEditor.LoadControlsFromContainer() ...
I can provide the rest of the stack trace if you need.

here is the ascx code:

<telerik:RadGrid ID="grdProspects" runat="server" AutoGenerateColumns="false" AllowMultiRowEdit="true">
    <ClientSettings EnableRowHoverStyle="true">
        <Scrolling AllowScroll="true" UseStaticHeaders="true" ScrollHeight="400" />
    </ClientSettings>
    <MasterTableView EditMode="InPlace" CommandItemDisplay="TopAndBottom">
        <CommandItemStyle Height="25px" HorizontalAlign="Right" />
        <CommandItemTemplate>
            <asp:LinkButton ID="lnkAddProspect" runat="server" CommandName="ADD_PROSPECT"><asp:Image ID="imgAddProspect" runat="server" ImageUrl="~/DesktopModules/BAOffice/images/ADD.gif" ToolTip="Add New Prospect" />&nbsp;Add New Prospect</asp:LinkButton>
            &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
            <asp:LinkButton ID="lnkSaveProspects" runat="server" CommandName="SAVE_PROSPECTS"><asp:Image ID="Image1" runat="server" ImageUrl="~/DesktopModules/BAOffice/images/save.gif" ToolTip="Save Changes" />&nbsp;Save Changes</asp:LinkButton>
            &nbsp;&nbsp;
        </CommandItemTemplate>
    </MasterTableView>
</telerik:RadGrid>

here is the vb code:

 Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
            If Not IsPostBack Then

              For Each column As SourceColumn In MyProspectEditor.SourceColumns

                Dim boundColumn As New GridBoundColumn()
                boundColumn.DataField = column.Name
                boundColumn.HeaderText = column.Name
                boundColumn.ReadOnly = column.IsReadOnly
                grdProspects.MasterTableView.Columns.Add(boundColumn)

               Next

            End If
        End Sub

#Region " Prospects "

        Private Sub grdProspects_ItemCommand(ByVal source As Object, ByVal e As Telerik.Web.UI.GridCommandEventArgs) Handles grdProspects.ItemCommand

            Select Case e.CommandName.ToUpper

                Case "SAVE_PROSPECTS"


                Case "ADD_PROSPECT"

            End Select
        End Sub



        Private Sub grdProspects_NeedDataSource(ByVal source As Object, ByVal e As Telerik.Web.UI.GridNeedDataSourceEventArgs) Handles grdProspects.NeedDataSource
            If MyProspectEditor IsNot Nothing Then
                grdProspects.DataSource = MyProspectEditor.GetWorkingData()
            End If
        End Sub

        Private Sub grdProspects_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles grdProspects.PreRender
            If Not IsPostBack Then
                For Each item As GridItem In grdProspects.MasterTableView.Items
                    If TypeOf item Is GridEditableItem Then
                        Dim editableItem As GridEditableItem = CType(item, GridDataItem)
                        editableItem.Edit = True
                    End If
                Next
                grdProspects.Rebind()
            End If

        End Sub

Any ideas?
thanks!

[Dave]

OK, i found my problem. I was not adding the columns to the mastertableview first before adding the properties. As soon as i switched the order, everything worked correctly.