"PAM unable to resolve symbol"

Good morning,
one of my systems sporadically log the following error messages:

----------------------------------------------------------------
PAM unable to resolve symbol: pam_sm_open_session
PAM unable to resolve symbol: pam_sm_close_session
----------------------------------------------------------------

The problem is not reproducable yet, since I do not know what could be 
going wrong.
The whole context in /var/log/auth looks like following:
----------------------------------------------------------------
Mar 25 06:45:21 Atlas sudo:   zabbix : TTY=unknown ; PWD=/ ; USER=root ; 
COMMAND=/usr/sbin/smartctl -a /dev/sdf
Mar 25 06:45:21 Atlas sudo: pam_unix(sudo:session): session opened for 
user root by (uid=103)
Mar 25 06:45:21 Atlas sudo: pam_unix(sudo:session): session closed for 
user root
Mar 25 06:45:26 Atlas auth: PAM unable to resolve symbol: 
pam_sm_open_session
Mar 25 06:45:26 Atlas auth: PAM unable to resolve symbol: 
pam_sm_close_session
Mar 25 06:45:26 Atlas auth: PAM unable to resolve symbol: 
pam_sm_open_session
Mar 25 06:45:26 Atlas auth: PAM unable to resolve symbol: 
pam_sm_close_session
Mar 25 06:45:26 Atlas auth: PAM unable to resolve symbol: 
pam_sm_open_session
Mar 25 06:45:26 Atlas auth: PAM unable to resolve symbol: 
pam_sm_close_session
Mar 25 06:45:28 Atlas auth: PAM unable to resolve symbol: 
pam_sm_open_session
Mar 25 06:45:28 Atlas auth: PAM unable to resolve symbol: 
pam_sm_close_session
Mar 25 06:45:29 Atlas auth: PAM unable to resolve symbol: 
pam_sm_open_session
Mar 25 06:45:29 Atlas auth: PAM unable to resolve symbol: 
pam_sm_close_session
Mar 25 06:45:29 Atlas auth: PAM unable to resolve symbol: 
pam_sm_open_session
Mar 25 06:45:29 Atlas auth: PAM unable to resolve symbol: 
pam_sm_close_session
Mar 25 06:45:29 Atlas auth: PAM unable to resolve symbol: 
pam_sm_open_session
Mar 25 06:45:29 Atlas auth: PAM unable to resolve symbol: 
pam_sm_close_session
Mar 25 06:45:38 Atlas sshd[26057]: SSH: Server;Ltype: Version;Remote: 
10.0.0.2-57912;Protocol: 2.0;Client: zabbix_agent
Mar 25 06:45:40 Atlas sudo:   zabbix : TTY=unknown ; PWD=/ ; USER=root ; 
COMMAND=/usr/sbin/iptstate -1
Mar 25 06:45:40 Atlas sudo: pam_unix(sudo:session): session opened for 
user root by (uid=103)
Mar 25 06:45:40 Atlas sudo: pam_unix(sudo:session): session closed for 
user root
----------------------------------------------------------------
These entries occur at different times, so I can not recognize a pattern 
or a system or something like that. Sometimes the error occurs a few 
times during a few hours, sometimes everything works well for 10 hours.

I use a hardened Gentoo Linux with kernel 3.0.4-r1, pambase-20101024-r2 
and pam-1.1.5. Of course I reinstalled these packets and all their 
dependencies, but this had no effect at all.

Any help would be really appreciated.

Best regards,
Yann