Starting from jboss-4.0.2 the default class loading for webapps has changed.

jbossweb-tomcat55.sar/META-INF/jboss-service.xml

UseJBossWebLoader=false

which isolates webapps from other deployments. Try using UseJBossWebLoader=true for a single LoaderRepository.

More to that is given here
http://wiki.jboss.org/wiki/Wiki.jsp?page=ClassLoadingConfiguration