Unable to update a checkbox in gridview, adding works fine object null reference

Hello,
I have a check box in a editable gridview, I can add new records fine with the text fields and checkbox but when I go to update an existing record in the rowupdating event of gridview it keeps giving object reference null for chkBoxDSA as if it's not finding the checkbox for editing. Here is the HTML code for the checkbox from the gridview markup.
<asp:TemplateField HeaderText="DefaiultShipLocation">
<ItemTemplate> <asp:Label ID="lblDefaultShipLocation" runat="server" Text='<%#Eval("DefaultShipLocation") %>'></asp:Label> </ItemTemplate>
<EditItemTemplate> <asp:CheckBox ID="ChckBxDefaultShipLocation" runat="server"></asp:CheckBox> </EditItemTemplate> <FooterTemplate> <asp:CheckBox ID="ChckBxAddADefaultShipLocation" runat="server"></asp:CheckBox> ...