HI Pankaj Kejriwal....
Try This
IF @object_type = '17' and @transaction_type = 'U'
Begin
IF exists(SELECT T0.DOCENTRY from ORDR T0 WHERE
T0.DocEntry = @list_of_cols_val_tab_del and T0.usersign2 in ('27','28'))
Begin
Set @error = 1
Set @error_message = N'Sales Order Not allowed to edit'
END
END
Hope helpful 
Regards
Kennedy