I recently migrated 10 mailboxes from 1 DB to the another and they completed successfully but after the move the migration tab in EAC didn't work. It would generate an error when I clicked on it. I went to view the DBs and found that one had dismounted and wouldn't mount. I ended up repairing the DB and now I'm able to mount it and also able to open the Migration tab again BUT when I attempt a mailbox migration it doesn't queue it. I click on the Migration tab in EAC and it's empty. No errors.