[23790] dbg: received-header: unknown format: from iron.psg.net ([unix socket]) by iron (Cyrus v2.1.18-IPv6-Debian-2.1.18-3) with LMTP; Mon, 19 Jun 2006 20:42:38 -0700
The problem is probably the [unix socket] part, at a guess. If you can do something about that it would probably help.
Even with the headers unparsable you should still be getting scored on spams. You probably won't get as much score as you should since it won't be able to apply a number of network tests correctly.
Try running 'spamassassin --lint' and see if it complains about anything. Remember to do this as whichever user normally runs SA.
Loren