When Distributed FileManager/MVS detects an error while processing a DDM command, the appropriate architected DDM error reply message is sent back to the source system that generated the DDM command stream. The reply message contains a server-diagnostic-information field (SRVDGN) and an error code. The server-diagnostic-information field of the error reply message contains up to 255 bytes of diagnostic data. This data can be used to correlate the error with a dump, LOGREC record, or other diagnostic information.

By using the error codes, source system users or MVS system programmers will be able to determine actions necessary to resolve the error. For example, the returned reply message FILNFNRM means "file not found". This means that the command processor failed to find the file because it does not exist on the MVS system. The end user issuing the request may or may not anticipate such a response as normal depending on the application logic. Another possibility could be that the specified file was not found because the file name input in the DDM command was misspelled.