A common ED501 message is “WARNING: SUBSTITUTION TABLE ENTRY NOT FOUND”. This substitution table is maintained in screen ED40.1, and if the key values passed to ED501 are missing, you will receive this error. Simply update your ED40.1 and recover the job.
If this message causes your job to go into recovery, that is because you have not set up notifications for EDI. If you set up notifications, then this message will cause an email to be sent about the warning, but the job will continue to process the remaining files. Notifications are configured on ED00.1, as well as the configuration file located in the EDI directory.