Unstable error messages in services with trace enabled

Sometimes it reproduced with the following case:

`fbsvcmgr service_mgr -user SYSDBA -action_backup -dbname employee -bkp_file /a/test_db_backup.fbk`

Usually, only one error message appears (cannot open backup file in this case), but with trace enabled, a second error sometimes appears (-Exiting before completion due to errors in this case).
