Index out of Range Exception

In Gridview Add the Property As DataKeyNames="value" 

that value is representation for your column name.

protected void grdClientDetails_RowDeleting(object sender, GridViewDeleteEventArgs e)
   {
 
       int int32Id = Convert.ToInt32(grdClientDetails.DataKeys[e.RowIndex].Value);
 
       ClsClientReg obj = new ClsClientReg();
       obj.DeleteClient(int32Id);

       obj.SubmitChanges();
 
   }