Tomcat has changed a litle bit it's StandardClassLoader from version 5.0.x to 5.5.x

http://jakarta.apache.org/tomcat/tomcat-5.0-doc/catalina/docs/api/index.html
   object - *org.apache.catalina.loader.StandardClassLoader*
and


http://jakarta.apache.org/tomcat/tomcat-5.5-doc/catalina/docs/api/index.html
   object - *org.apache.catalina.loader.StandardClassLoader

The StandardClassLoader in 5.5 is now a subclass of URLClassLoader, so a hybrid of the alternate style of loading classes in the embedded OpenEJB scenario should work. Some work has been done to get classes loaded, however this seems to cause other class cast related issues.