Whats wrong wiht this code? Invalid cast

[MrNorth]

Dim chkBox As New CheckBox
        Dim oOrder As New COrder
        For Each di As DataGridItem In dgOrders.Items
            chkBox = CType(di.Cells(4).Controls(0), CheckBox)
            If chkBox.Checked Then
                oOrder.CloseOrder(di.Cells(0).Text)
            End If
        Next

This code occurs when I hit a save button and it checks which checkboxes in the grid that was checked and update the db (oorder.closeorder)

but the line

chkBox = CType(di.Cells(4).Controls(0), CheckBox)

doesn't work, I get an invalid cast exception... why? is there any other way to do it?

kind regards
henrik