Can't login: no pam_unix.so found

[Victor Star]

Hi guys,

I need your help to fix my FreeBSD 6.2-RELEASE system.
This is my home server, used mostly for mail (courier) and local file server (samba).
It's been up for quite some time with no problems and really fun for me to learn FreeBSD.
I've learned lots of things configuring postfix, courier, RAIDs and wireless.
But now I have something I can't handle myself. Spent time searching archives, web to no avail.

Now, few days ago I started getting the following in the daily security run output:

====- 8< -===================================================
Checking for packages with security vulnerabilities:

su: pam_start: system error
====- 8< -===================================================

What I see on the console is:
====- 8< -===================================================
su: in openpam_load_module(): no pam_unix.so found
su: pam_start: system error
====- 8< -===================================================

I can't also login neither through ssh nor on the console - getting same error.
Luckily I still have one ssh root session alive (so far!). 
I have this bad feeling that on disconnect or reboot I will loose the access to the box.

Mail server still working no problem, smtp and POP via SSL work and authorize fine.

pam_unix.so is in /usr/lib:
====- 8< -===================================================
# ls -l /usr/lib/pam_unix*
lrwxr-xr-x  1 root  wheel     13 Sep 25  2006 /usr/lib/pam_unix.so -> pam_unix.so.3
-r--r--r--  1 root  wheel  10240 Feb 19  2007 /usr/lib/pam_unix.so.3
# file /usr/lib/pam_unix.so
/usr/lib/pam_unix.so: symbolic link to `pam_unix.so.3'
====- 8< -===================================================

There is one more thing that is suspiciously close in time to when this started happening.
In the same security run output where  I first saw this error I found this:
====- 8< -===================================================
Sep 18 11:11:37 xxxxxx su: BAD SU <myloginname> to root on /dev/ttyp3
Sep 18 11:13:46 xxxxxx sshd[45047]: Bad protocol version identification '\377\364\377\375\006quit' from <some ip here>
Sep 18 11:15:08 xxxxxx sshd[45056]: Received disconnect from <some ip here>: 2: Bad packet length 710099706.
====- 8< -===================================================

I'd appreciate any ideas about what happened and how to get it fixed.

Thanks!
  
-- 
Best regards,
 Victor