Restrict user to Edit the Sales Order thru SP

Dear Expert,

                   I have applied the following query to Restrict user to Edit the Sales Order thru SP.But the SP is blocking all the user in the database.

Kindly suggest some solution for it.

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.usersign  in ('27','28'))

      Begin

            Set @error = 1

            Set @error_message  = N'Sales Order Not allowed to edit'                

      END

END

regards,

PankajK

IDM Services Ltd.