Problem with PAM/LDAP auth

I am trying to set up PAM-auth for a small testing system but I am stuck
with a strange problem.

The system authenticates OK (both login and ssh can authenticate using the
LDAP accounts) but trying to login to the same account to postgresql fails.
I have setup a login role with the same name and authenticating against
postgresql as that user works. my pg_hba.conf looks like this:

local all postgres ident sameuser
local all all ident sameuser
host all all 127.0.0.1/32 md5
host ip_cis nagios xx.116.13.224/27 md5
host ip_cis all xx.116.13.224/27 pam

I try to connect as:
psql -h cis.ipxxx.at -U tkircht -d ip_cis

My log (debug level 5) comes up with those lines even before I entered a
password:

2009-07-08 21:28:06 CEST LOG: 00000: connection received:
host=xx.116.13.253 port=47092
2009-07-08 21:28:06 CEST LOCATION: BackendInitialize, postmaster.c:3027
2009-07-08 21:28:06 CEST LOG: 00000: pam_authenticate failed: Permission
denied
2009-07-08 21:28:06 CEST LOCATION: CheckPAMAuth, auth.c:1345
2009-07-08 21:28:06 CEST FATAL: 28000: PAM authentication failed for user
"tkircht"
2009-07-08 21:28:06 CEST LOCATION: auth_failed, auth.c:1003

my pam stack looks (after many other attempts) like this:

auth sufficient pam_ldap.so

This suggests some problems accessing some pam-related file but I cannot
imagine which one?

The server runs on Debian 5 by the way.

Any pointers would be highly appreciated - the PostgreSQL documentation is
pretty thin on this..

Thanks!

Thomas