Today out of the blue I started getting the following warning on one of my Exchange Servers:
Mailbox cleanup could not completely remove the mailbox for user following mailbox removal. Encountered error 0xfffffae8. Should this message continue to persist for the same mailbox, it may be indicative of a problem that requires further investigation.
So no mailbox moves or removals have been done in about 8 months but to clear the warning from logging in event viewer every minute is to just dismount the database and mount it again.
The warnings will be gone, maybe a bug of some sorts?
Hope it helps.