The job failed. It had been working forever and suddenly it wasn't any more. There was of course no documentation - well you knew that. There was no description in the job description. It ran an obscurely named stored procedure.
Okay, the SP connected to an entirely different server, extracted some data from a database that didn't exist, and sent it to an unknown FTP server. Well, extracting something from a database that doesn't exist (having been dropped yesterday) probably explains why the job was failing today.
The database in question was for a client we stopped working with about five years ago. And looking at the history it seemed likely that we had been extracting nothing for those five years, encrypting the nothing, and sending it to the client that we no longer worked with. Somewhere in the former client's IT department there must be a bod wondering about his error message...
Asking around, one of the developers remembers the customer wanting us to encrypt an empty file and ftp it to them, even though the customer had no business for us. Something about keeping a gateway open just in case...