From your description I would guess that there's no proper 'SET ISOLATION' and 'SET LOCK MODE' combination issued for the application. If not issued within the application the default isolation level of the database is used. If other than 'DIRTY READ' and an explicit 'SET LOCK MODE TO NOT WAIT' is in effect I expect an error message like yours. But it would clear up things if you could post the accompanying errorcode as well.
Regards,