Concurrency anomolies with WebLogic and JTS

We are finding a series of anmolies with a WebLogic EJB application using a JTS (Java Transaction Service) driver. The Informix exception 604 minor 113 reads... <Informix error documention> -604 Cannot read TEXT or BYTE value. This statement refers to a BYTE or TEXT value, but some unexpected error prevented access to the value. Roll back the current transaction. Check the accompanying ISAM error code for more information; possibly a hardware error or data corruption of the storage space or tblspace occurred. If the error recurs, please note all circumstances and contact Informix Technical Support. -113 ISAM error: the file is locked. Another user request has opened the file (table) that was requested in exclusive mode. In systems that use files for locking, a tablename.lok file exists. Possibly such a file was left behind when another program terminated abnormally. If you are sure that is the case, you can release the lock by emptying that file. Lock files are not used in many systems, and they are never used with Informix Dynamic Server or INFORMIX-OnLine Dynamic Server. For C-ISAM programs, rerun the program after the file has been unlocked. For SQL products, tables are locked explicitly using the LOCK TABLE statement and implicitly during the execution of the CREATE INDEX or ALTER TABLE statement. Rerun the program or query when the table has been unlocked </Informix error documention> This exception is thrown randomly on a large automated load test. Is it possible that the release of the JTS lock is not properly propogated.... Any ideas welcome