Just to indicate some replication, I also experienced this in the last few days. Presumably it's just a incorrect version for the pam dependencies of the kdm package, or something like that.
I installed kdm 4.2.2-2 from Debian Unstable on my amd64 system, along with many other KDE4 packages. It left me with libpam0g 0.99.7.1-5. The KDM login screen would load fine, but whenever entered a username/password and tried to log in, I'd immediately get a pop-up error dialog indicating than an error had occurred and that I should check the KDM log file(s) for more information. (Unfortunately I don't have the exact error message text, but it wasn't very helpful.) The /var/log/kdm.log file didn't have any useful information, but I eventually discovered some suspect lines in /var/log/syslog that pointed to pam. Notably lines like: Apr 19 17:37:54 mira kdm_greet[9623]: Unknown V_xxx code 4 from core Apr 19 17:37:55 mira kdm: :0[9607]: PAM pam_setcred: NULL pam handle passed Apr 19 17:37:55 mira kdm: :0[9607]: pam_setcred() for izogi failed: System error Apr 19 17:37:55 mira kdm: :0[9607]: Client start failed Apr 19 17:37:55 mira kdm: :0[9607]: PAM pam_setcred: NULL pam handle passed Apr 19 17:37:55 mira kdm: :0[9607]: pam_setcred(DELETE_CRED) failed: System error [--snip--] Apr 19 17:38:09 mira kdm: :0[11203]: PAM error: Bad item passed to pam_*_item() When I upgraded libpam0g from version 0.99.7.1-5 to 1.0.1-0 and libpam-modules from 0.99.7.1-5 to 1.0.1-9 and the problems went away. (I already had libpam-runtime 1.0.1-9 from an earlier occasion before installing kdm 4.2.)
