dovecot - Sep 2003 - squirrelmail + dovecot + qmail + vpopmail error

ERROR : Could not complete request.
Query: COPY 99:99 "INBOX.SPAM"
Reason Given: [TRYCREATE] Mailbox doesn't exist: INBOX.SPAM

Running latest stable version of squirrelmail, dovecot, qmail and
vpopmail with Maildir storage in virtual users.

One of my users reports seeing this yesterday, then it went away for a
few hours, then early in the next day it happened again on the same
account, but went away a little while after that.

Any idea what could be happening here?

Warren Togami
warren at togami.com