[Dovecot] Broken header

[Jon]

Hi, I just upgraded to version 1.0.5 hoping to get rid of a problem that 
made Thunderbird download all mails from time to time. I now see this 
error (below). Does anyone know what it means?

Error: IMAP(user): 
/mail2/home/user/.Maildir/.Folders.Persons.Foldername/dovecot-uidlist: 
Broken header (uidvalidity = 0, next_uid=10)

Error: IMAP(user): 
/mail2/home/user/.Maildir/.Folders.2005/dovecot-uidlist: Broken header 
(uidvalidity = 0, next_uid=1186)

Mails are stored in userhomedirs that are located on a NFS export.

See below output from dovecote -n

[root at mail dovecot-1.0.5]# /usr/local/sbin/dovecot -n
# 1.0.5: /usr/local/etc/dovecot.conf
log_path: /var/log/dovecot.log
login_dir: /usr/local/var/run/dovecot/login
login_executable: /usr/local/libexec/dovecot/imap-login
login_processes_count: 2
mail_location: maildir:%h/.Maildir
mmap_disable: yes
auth default:
  passdb:
    driver: pam
  userdb:
    driver: passwd

Best Regards - Jon