[SM-USERS] Cannot delete messages

[<lsy...@2c...>]

Hi,
My company has been using squirrelmail for some time now with no problems, but today no one is able to delete messages.  There is an error given that says

ERROR : Could not complete request.
Reason Given: [ALERT] COPY failed - no write permission or out of disk space.

There is plenty of diskspace, and the permissions are good too.  

Anyone have an idea of what's going on or what else I should check?
Thanks