Are any of your other applications going wonky, or is it just Logic?
I'm afraid I've never heard of this particular problem before, but if it were happening to me the first thing I would do is delete my "com.apple.logic.express.plist" file in Library>Preferences, then repair permissions in Disc Utility, and finally restart my computer. Then I would launch Logic and see if the problem has been corrected. It's amazing how much these two steps can accomplish.
If that doesn't resolve the issue I would launch Logic and go to Preferences>Audio Units Manager to see if all my plug-ins are properly validated.