The problem is with the Last Modified date in the user's mail archive settings (I would have never guessed this had anything to with a mail file move, but apparently AdminP checks to see if the mail file has an archive, and if so, does it need to update the archive server specified). Go to Actions, Archive, Settings, Settings tab, make sure the last change entry is a valid user name (If your user had a cert rename, it will probably be their old name) If the Last Change field contains a user name that is no longer valid, then resave the settings so that a valid user name is placed in the Last Change field. Re-issue the mail file move so a new AdminP request gets generated (don't just re-run the existing adminP request) and the move should then complete successfully.
