Accessing checkbox in datagrid control - Specified cast is not valid.

Below is the error that I get when I try to access the checkbox in the data grid control.

after data grid binding I have the following code to loop through the dg control to check or leave unchecked the checkboxes.  However I get the error message described below.  Specified cast is not valid. What do I do?  Please help.  It was worked in the past but not working now.  i checked the html code and that is all fine as well.  Even more odd is that casting a listbox an delecting items in the same datagrid control works.  Just not the checkboxes.

  For i = 0 To dg1a.Items.Count - 1
            flag = sqlDst.Tables("poe_data_cleaning").Rows(i)(2)
            If flag = 1 Then
                 CType(dg1a.Items(i).FindControl("cb1a"), Checkbox).Checked = True
             End If
            If flag = 0 Then
                CType(dg1a.Items(i).FindControl("cb1a"), Checkbox).Checked = False
            End If

Specified cast is not valid.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidCastException: Specified cast is not valid.

Source Error:

Line 341:            If flag = 1 Then
Line 342:                CType(dg1a.Items(i).FindControl("cb1a"), Checkbox).Checked = True

Source File: C:\Inetpub\wwwroot\POE\PoeBuildModelTab.aspx.vb    Line: 343

Stack Trace:

[InvalidCastException: Specified cast is not valid.]
   POE.PoeBuildModelTab.LoadExistingData() in C:\Inetpub\wwwroot\POE\PoeBuildModelTab.aspx.vb:343
   POE.PoeBuildModelTab.Page_Load(Object sender, EventArgs e) in C:\Inetpub\wwwroot\POE\PoeBuildModelTab.aspx.vb:69
   System.Web.UI.Control.OnLoad(EventArgs e) +67
   System.Web.UI.Control.LoadRecursive() +35
   System.Web.UI.Page.ProcessRequestMain() +750

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what is there on line 343
dmontgomAuthor Commented:
solved problem  request refund
dmontgomAuthor Commented:
a 3rd party control was messing up stuff

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