Here is The Solution..
Define CustomerID Field as follows..
Inside EditItemTemplate
<columns>
<asp:TemplateField HeaderText="Country ID" >
<itemtemplate>
<%#Eval("Country_id")%>
</itemtemplate>
<edititemtemplate>
<asp:Textbox id="txtCountry_id" runat="server" Enabled="false">
Text='<%#Eval("Country_id")%>'>
</edititemtemplate>
</columns>
Later If You Will Have Doubts Just Replay Me...