Just to check, which JVM are you using? What is the output of 'java -version'?Did you make sure that both Tomcat and Derby where using the same JVM?This seems to be irrelevant.
Well, if he uses a default Kaffee or gij, there are many classloader issues with Tomcat. I already had several users having problems with Sequoia and Derby because of the wrong JVM.
Emmanuel
