Thanks for your all of your help.

When a row is first queued, the row is successfully processed, but then it
seems to attempt to be processed 5 more times until the queue is disabled.
In the following snippet, the raiserror causes an exception five times after
the first successful process.  This does not occur when "with cleanup" is
part of the "end conversation" command.  I know I'm doing something wrong,
but can't figure out what.

   begin try;
       begin transaction;

       waitfor
       (
           receive
               top( 1 )
               @ConversationHandle   = conversation_handle,
               @QueueMessage = message_body
           from
               q_Request
       ), timeout 12000

       if @@rowcount !> 0
       begin
           rollback
           return @ERROR_NOTHINGQUEUED
       end

       if @QueueMessage is null
           raiserror ( 'null queue message error', 18, 5 )

       end conversation @ConversationHandle --with cleanup

       commit
   end try

   begin catch
       rollback
       exec dbo.p_ExceptionLog
       return @ERROR_UNHANDLEDEXCEPTION
   end catch