Archived files go to "Failed External Filter" folder.
I recently enabled a user's account for archiving, but whenever she tries to manually archive, the clock appears over the message and then the message goes into "Failed External Filter". I checked the security logs on the EV server and it shows the user successfully logging in/out. Just the one user.
Also, whenever the user tries to archive the following error pops up in the event viewer on the EV server: error 3263: "An error occurred processing the external filter 'EnterpriseVault.CustomFilter'. No more filters will be processed."