Nope, would you believe 2003 which they upgraded from 5.5. Like I said, this is a total mess which is why we've just told them to sod off when they wanted to upgrade to 2007. We'll build a brand new cluster and migrate the mailboxes properly.

Error codes starting with 5 are permanent errors which won't resolve without investigation. 4 code errors are "it may possibly resolve itself" errors. Trust me, I spent a LOOOOOOONG time on Google trying to fix this. Just glad it is though as it stops about 9 service calls being peppered to me.