Tomcat 4 by chance? Are you compiling a lot of JSPs?
If yes to both questions you're running into a known bug in the JSP compiler in Tomcat 4. Restarting Tomcat (make sure you have not set it to throw away compiled JSPs on exit) is all that's needed. Or upgrade to Tomcat 4 which has supposedly had this fixed.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus