I would guess that you are using the JVM that comes with gentoo. To verify this, enter "java -version" and post the response. Anyway, you need a JVM from Sun (or JRockit) to run JBoss.
I already posted my java -version but here it is again:
HPNETSERVER3 jboss2 # java -version java version "1.4.2-03" Java(TM) 2 Runtime Environment, Standard Edition (build Blackdown-1.4.2-03) Java HotSpot(TM) Client VM (build Blackdown-1.4.2-03, mixed mode)
I gues that my emerge jboss installation changed the 'default' Gentoo java JRE to the Blackdown JRE or is Blackdown the default Gentoo JRE?
Sorry, I missed the version text in your post, only saw the stack dump. This is not a Sun JVM, you should download one and use it.
I've got the new jdk and Jboss works