dovecot - May 2006 - auth: pam_setcred() failed: Error in service module

Hi,

I have a strange problem with authentication. Some users can
successfully authenticate and some users can not authenticate.
All users use the same client (thunderbird-1.5.0.2-win32-de).
At the problematic users i get the following error message:

============ snip ================== auth(default): client in: AUTH     8	PLAIN 
service=IMAP    secured lip=10.24.1.6   rip=10.211.11.1
 auth(default): client out: CONT    8
 auth(default): client in: CONT<hidden>
 auth(default): pam(pgerlesb,10.211.11.1): pam_setcred() failed: Error in
service module
 auth(default): client out: FAIL    8	user=pgerlesb
 auth(default): client in: AUTH     9	PLAIN   service=IMAP    secured
lip=10.24.1.6   rip=10.211.11.1 resp=<hidden>
 auth(default): pam(pgerlesb,10.211.11.1): pam_setcred() failed: Error in
service module
 auth(default): client out: FAIL    9	user=pgerlesb
 imap-login: Aborted login: user=<pgerlesb>, method=PLAIN,
rip=10.211.11.1, lip=10.24.1.6, TLS
============ snap ==================

The username and password is right. I can "su - <username>" at
the
dovecot host with the same password. Some other users can authenticate
without any problems.

I have set in dovecot.conf:

	auth default {
	  mechanisms = plain
	  passdb pam {
	    args = "*"
	  }
	  userdb passwd {
	  }
	}



I have configured PAM to do the authentication against Kerberos5. The
user data come from an LDAP directory.

What could be the problem?

Thanks
Martin Stockinger