[Dovecot] Dovecot lock problem

Hi,

We have a few users experiencing locking problem. When starting Thunderbird, there is no new emails in Inbox. Dovecot createa a lock file /var/spool/mail/<user>.lock. It never completes openning Inbox. If closing the mail client, the open imap session does not get closed, nor the lock file get deleted.

Here are the errors in log:

dovecot: Oct 13 11:18:35 Warning: IMAP(user1): Our dotlock file /var/mail/user1.lock was deleted (kept it 88 secs) dovecot: Oct 13 11:18:35 Error: IMAP(user1): file_dotlock_delete() failed with mbox file /var/mail/user1: No such file or directory

We are running Dovecot 1.1.2. Any pointer to resolve this problem is appreciated.

Simon