http://docs.info.apple.com/article.html?artnum=55743 says it's a memory or an extensions problem (there was a problem with old FaxStf extensions).

If you need to rule out a physical RAM problem, there are some memory checking utilities available, like the one on the AppleCare CD (TechToolPro). Maybe Google can help with something like http://www.macupdate.com/info.php/id/4512