Hi Ravi,
Please don't forget to add the DataKeyName="PrimaryKeyField" property in the grid view like
<asp:gridview id="Gridview1" run="server" datakeynames="CustID" >
int uid = (int)gvDeleteUser.DataKeys[gvDeleteUser.Rows.RowIndex].Value;
Please check it and let me know in case of any concerns.
And please make it as resolved if it resolves.
Thanks and Regards
Suman Zalodiya