dovecot help?

[I Rattan <ratta1i@cps.cmich.edu>]

Trying to make dovecot-imap server run under linux
(Linux tigaon 2.6.25-4.slh.3-sidux-686 #1 SMP PREEMPT Fri May 23 21:58:49 
\
UTC 2008 i686 GNU/Linux)

The following config generates the error:
dovecot: Aug 18 13:33:51 Error: auth(default): passwd-file /etc/passwd: \
User root has invalid UID 0)

but if some other is used it can't access the /etc/shadow file!!

Any pointers?
-----/etc/dovecot/dovecot.conf---
base_dir = /var/run/dovecot/
protocols = imap
log_path = /var/log/dovecot
info_log_path = /var/log/dovecot.info
login_dir = /var/run/dovecot/login
login_chroot = yes
login_user = dovecot
protocol imap {
  login_executable = /usr/lib/dovecot/imap-login
  mail_executable = /usr/lib/dovecot/imap
}
valid_chroot_dirs = /var/spool/vmail
default_mail_env = maildir:/home/vmail/%d/%n
disable_plaintext_auth = no
auth default {
  mechanisms = plain login digest-md5
  userdb passwd-file {
        args = /etc/passwd
      }
  passdb passwd-file {
          args = /etc/shadow
      }
}
auth_executable = /usr/lib/dovecot/dovecot-auth
auth_user = root
auth_verbose = yes
---