This is mentioned in the forums but I thought I'd let you know.
Apparently it's because the guy at JBoss that created the build, compiled it against a 1.5 JDK.
I'm therefore guessing you're using a 1.4 or less JDK version to execute this?
I've tried compiling the 3.0.1 build against 1.4 myself but I started to get docbook dependancy problems - so couldn't be bothered. I myself have reverted to the version 3.0 distribution for now.
Let me know if you come up with a solution.
Just to add - I actually now have a newly compiled 3.0.1 version working - it just takes some playing around with the JAR file locations.