I have experienced the same problem with JBoss 3.2.5. As a work-around I need to restart JBoss one or more times and redeploy my project also one or more times.
I posted the problem in the MyEclipse forum. The support there suggested an incompatibility in JBoss with several Jar files containing the same class with differing methods. I would suggest registering the problem with JBoss as a bug.
I got the same error when I first deployed the jcatalog in jboss 3.2.7, however, after deleting the servlet.jar in the jcatalog.war/WEB-INF/lib, it looked fine. hope it helps.