Can't archive mail on one of my Exchange accounts

I have a few Exchange accounts set up in Mail that are working fine. Deleting sends the mail to the Trash folder, archiving sends the mail to the Archive folder. However, one of the accounts won't let me archive. The mailbox has a folder under the "Archive" section on the sidebar, and I can manually drag messages to it, but when I click Archive I get the following: **The message “[subject]” could not be moved to the mailbox “(null)”** **The destination mailbox does not exist.** I would assume this means that Mail can't find the appropriate folder to put the message in, but since the account has a folder under the Archive heading, I'm confused. Any ideas?