I have a Macbook Pro running OSX 10.5.1 and Spamsieve 2.6.5. I have had problems recently with not being able to shut down properly (something preventing normal shutdown) - meaning I have to force a shutdown and get the error message when I next boot up.
Recently I have rebuilt my Macbook Pro from scratch and as I have added software I have tested this issue load by load. It only reoccurrred when I reinstalled Spamsieve. I removed all the Spamsieve components - problem went away. Reloaded, problem returned.