[Dovecot] Permission denied problems

[shacky]

Hi.
I'm trying to configure Dovecot for Vpopmail.
The authentication works good, but I have some "permission denied"
error when I try to open the IMAP folders:

dovecot: 2009-02-03 19:16:08 Info: imap-login: Login:
user=<test at testdomain.com>, method=PLAIN, rip=192.168.246.45,
lip=172.16.4.106, TLS
dovecot: 2009-02-03 19:16:09 Error: IMAP(prova at tuttoenumero.it):
stat(/home/vpopmail/domains/testdomain.com/test/Maildir/cur) failed:
Permission denied

This is my dovecot.conf:

protocols = imap imaps
disable_plaintext_auth = no
log_path = /var/log/dovecot.log
log_timestamp = "%Y-%m-%d %H:%M:%S "
login_greeting = IMAP server ready.
mail_location = maildir:/home/vpopmail/domains/%d/%n/Maildir
mail_privileged_group = vchkpw
mail_access_groups = vchkpw
mail_debug = yes
mmap_disable = yes (my maildirs are on a NFS filesystem)
first_valid_uid = 89
last_valid_uid = 89
first_valid_gid = 89
last_valid_gid = 89
auth_verbose = yes
auth_debug = yes
auth default {
  passdb vpopmail {
  }
  userdb passwd {
  }
  userdb static {
    args = uid=89 gid=89 mail=Maildir:/home/vpopmail/domains/%
  }
  userdb vpopmail {
  }
  user = vpopmail
}

The /home/vpopmail/domains directory and subdirectories are owned by
vpopmail.vchkpw and with the permissions 700. The user vpopmail can
access to /home/vpopmail/domains/testdomain.conf without any problem.

Could you help me to find the problem, please?

Thank you very much!
Bye.