After having tinkered with standalone .WAR YT in JBoss 5.1.0 GA I may have found a solution for the ClassLoader exceptions that get thrown on several occasions.
The problem is that there are some libraries in the .WAR (/WEB-INF/lib/) that are colliding with older versions of the same libs in JBoss (at a higher path). JBoss tries to use its own libs that fail for certain operations.
There is a neat and controlled way to disable the container's libs and favor the .WAR's version in cases of a collision: by adding a file "jboss-classloading.xml" in the /WEB-INF/ directory.
I've added an example of this file, and here are some URLs to articles explaining how it works:http://www.mastertheboss.com/jboss-configuration/solving-jboss-5-classloading-issueshttp://phytodata.wordpress.com/2010/10/21/demystifying-the-jboss5-jboss-classloading-xml-file/