dovecot - May 2013 - dovecot 1.2.5 Fatal: setgid(5000(vmail)) Operation not permitted

This is the error I'm getting (whenever i recieve and email):
*deliver() : Fatal: setgid(5000(vmail)) failed with euid=5000(vmail),
gid=8(mail), egid=8(mail): Operation not permitted (This binary should
probably be called with process group set to 5000(vmail) instead of 8(mail))
*

I am at loss. I have tried "everything" i could think of (besides
purging
the machine and do it all over again, which is not an option -- unless it
is). Can anyone help me fix this?

# 1.2.15: /etc/dovecot/dovecot.conf
# OS: Linux 3.2.13-grsec-xxxx-grs-ipv6-64-vps x86_64 Debian 6.0.6 ext3
log_timestamp: %Y-%m-%d %H:%M:%S
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
verbose_proctitle: yes
mail_uid: vmail
mail_gid: vmail
mail_location: maildir:/var/zpanel/vmail/%d/%n
mail_debug: yes
mbox_write_locks: fcntl dotlock
auth default:
  mechanisms: plain login
  verbose: yes
  debug: yes
  debug_passwords: yes
  passdb:
    driver: sql
    args: /etc/dovecot/dovecot-sql.conf
  userdb:
    driver: sql
    args: /etc/dovecot/dovecot-sql.conf
  socket:
    type: listen
    client:
      path: /var/spool/postfix/private/auth
      mode: 432
      user: postfix
      group: postfix
    master:
      path: /var/run/dovecot/auth-master
      mode: 432
      user: vmail
      group: vmail
plugin:
  trash: /etc/dovecot/dovecot-trash.conf

# /etc/dovecot/dovecot-sql.conf

driver = mysql
connect = host=localhost dbname=zpanel_postfix user=USERNAME
password=AWESOMEPASSWORD
default_pass_scheme = PLAIN
password_query = \
  SELECT name, domain, password \
  FROM mailbox WHERE name = '%n' AND domain = '%d'
user_query = \
  SELECT maildir \
  FROM mailbox WHERE name = '%n' AND active = '1' AND domain =
'%d'

#This is my ls -la
drwxrwsrwx  5 vmail vmail 4096 May  2 18:39 vmail

#and this is inside vmail/
drwx--S---  3 vmail vmail 4096 May  2 18:39 asfaltotejo.com
drwx--S---  3 vmail vmail 4096 May  2 12:35 gestaoconteudos.pt
drwx--S--- 17 vmail vmail 4096 May  2 15:34 tribanet.com

#/var/run/dovecot
srw-rw----  1 vmail vmail      0 May  2 19:46 auth-master
srw-------  1 root  root       0 May  2 19:46 auth-worker.6564
srwxrwxrwx  1 root  root       0 May  2 19:46 dict-server
lrwxrwxrwx  1 root  root      25 May  2 19:46 dovecot.conf ->
/etc/dovecot/dovecot.conf
drwxr-x---  2 root  dovecot 4096 May  2 19:46 login