I had a similar problem, and I found that the answer to my problem was to uninstall the webmail module. It makes some calls to java packages that must be downloaded from Sun's website and then loaded by hand (as is very well documented in the webmail module). If the classes aren't present, oracle's internal JVM runs amok.
The problem is also solved if you install the appropriate java classes they are: javamail, and the Java Activation Famework .
Don't know if this will help you or not...