[Dovecot] Dovecot Problem

[Robert Sloan]

Every 2 or 3 days dovecot will not allow me to log into my IMAP server.  
It keeps requesting my username and password.  If I do a 
/etc/init.d/dovecot restart it will start working again for a few days.  
I have dovecot set up to use Maildir.

Dovecot Version: Not sure but it is the one that comes with Ubuntu 9.04
OS: Ubuntu 9.04
CPU: x86
Filesystem: Local EXT4
Dovecot Config:

# 1.1.11: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.28-11-server i686 Ubuntu 9.04
log_timestamp: %Y-%m-%d %H:%M:%S
protocols: imap imaps pop3 pop3s
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable(default): /usr/lib/dovecot/imap-login
login_executable(imap): /usr/lib/dovecot/imap-login
login_executable(pop3): /usr/lib/dovecot/pop3-login
mail_privileged_group: mail
mail_location: maildir:~/Maildir
mail_executable(default): /usr/lib/dovecot/imap
mail_executable(imap): /usr/lib/dovecot/imap
mail_executable(pop3): /usr/lib/dovecot/pop3
mail_plugin_dir(default): /usr/lib/dovecot/modules/imap
mail_plugin_dir(imap): /usr/lib/dovecot/modules/imap
mail_plugin_dir(pop3): /usr/lib/dovecot/modules/pop3
auth default:
  passdb:
    driver: pam
  userdb:
    driver: passwd


Thanks.