procedure Scrn_duplicate is

Begin
 
   Declare
         Rec_no Number;
         Acccode Char(5);

   Begin
        Rec_no  := :System.Cursor_Record;
        Acccode := :YourFormname.Account_code;

        First_record;

        :global.dummy := '   ';        
        Loop

            If :System.Last_record = 'TRUE' then
                exit;
            End If;
            If :System.Cursor_Record = Rec_no Then
               exit;
            end if;
            If :YourFormname.Account_code = Acccode Then
                Messager('Duplicate Entry');
                :global.dummy := 'Error';
                exit;
            End If;
          Next_record;
        End Loop;
  End;
End;