[Dovecot] mbox problems on CentOS 6

[DT]

Hello,
I migrated yesterday to Dovecot 2, and I managed to "convert" all the settings I had in dovecot.conf, but I run into a strange problem. I am curently using Dovecot 2.0.13 and bellow is my dovecot.conf current content:
 
# 2.0.13: //etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-71.29.1.el6.x86_64 x86_64 CentOS Linux release 6.0 (Final) ext4
auth_mechanisms = plain login
auth_verbose = yes
base_dir = /var/run/dovecot/
disable_plaintext_auth = no
first_valid_uid = 901
last_valid_uid = 901
log_path = /var/log/dovecot.log
log_timestamp = "%Y-%m-%d %H:%M:%S "
login_greeting = IMAP/POP3 server ready.
mail_access_groups = mail
mail_debug = yes
mail_location = mbox:/vmail/%d/%n:INDEX=/var/indexes/%u
mail_max_userip_connections = 16
mail_privileged_group = mail
passdb {
  args = /etc/dovecot/dovecot-mysql.conf
  driver = sql
}
protocols = imap pop3
service auth {
  unix_listener auth-userdb {
    mode = 0600
  }
  user = $default_internal_user
}
service imap-login {
  inet_listener imap {
    port = 143
  }
}
service imap {
  process_limit = 16
}
service pop3-login {
  inet_listener pop3 {
    port = 110
  }
}
service pop3 {
  process_limit = 16
}
ssl = no
userdb {
  args = /etc/dovecot/dovecot-mysql.conf
  driver = sql
}
protocol pop3 {
  pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
  pop3_uidl_format = %08Xu%08Xv
}
protocol imap {
  imap_client_workarounds = delay-newmail tb-extra-mailbox-sep
}
 
I am running along with Dovecot, Postfix and MySQL - oh SASL is of course installed as I want to make use of user auth.
On the simplest check - "surprise" ta-daaaa
/telnet localhost 143
Trying ::1...
Connected to localhost.
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN AUTH=LOGIN] IMAP/POP3 server ready.
a login contact at mydomain.com mypassword
* BYE Internal error occurred. Refer to server log for more information.
Connection closed by foreign host.
I activated debug and looked in the dovecot logs and here is the most intriguing part I found:
auth: Info: mysql(localhost): Connected to database postfix
imap-login: Info: Login: user=<contact at mydomain.com>, method=PLAIN, rip=::1, lip=::1, mpid=5821, secured
imap: Debug: Added userdb setting: mail=maildir:/vmail/mydomain.com/contact
imap: Debug: Added userdb setting: plugin/quota=dirsize:storage=0
imap(contact at mydomain.com): Debug: Effective uid=901, gid=12, home=/vmail/mydomain.com/contact
imap(contact at mydomain.com): Error: user contact at mydomain.com: Initialization failed: Initializing mail storage from mail_location setting failed: Unknown mail storage driver maildir
imap(contact at mydomain.com): Error: Invalid user settings. Refer to server log for more information.
 
I double checked paths - all is ok - postfix is actually receiving and saving in that /vmail... folder
# uid=901 coresponds to <vmail> user
# gid=12 corresponds to <mail> group
# rights on /vmail are vmail.mail
 
I think there is actually a problem with mail_location - but I couldnt solve it at all. If anyone can help me with this - please do guys. I googled those terms and found nothing, so this is my last resort, I tried solving this in the last 36hrs but nothing so far.
 
Thanks to anyone who can assist me.