Warren:

I have seen a client where they would get this message a few times a week. It was caused by the same thing: a temporary index file that shouldn't have been there. The Adagio processes weren't expecting to find an index file when the matching data file didn't exist.

The problem was that when a matching pair of temporary files were created for a process, both files should have been deleted. But in fact, the data file was deleted but not the matching index file.

Eventually they replaced the server and the problem disappeared. But if this is an entirely isolated incident for your client, the explanation might be different.