Can't archive mail on one of my Exchange accounts

Solution 1:

I had the same problem. I went into Preferences > Accounts and deselected "Enable this account." Then, I quit Mail and restarted it. I went back into Preferences > Accounts and selected "Enable this account" and it all started working.

Solution 2:

Rename the Archive folder on Exchange

Seems some sort of bad situation manifested itself between Mail and the Exchange server. I had to Rename the folder named Archive on the server to OldArchive, then attempt to archive a message and allow Mail to recreate the Archive folder. Then I copied all the mail in OldArchive to the new Archive.