I believe that Eclipse make problems, because I publish application of JBoss, using some plug-ins. Eclipse automatically add ligraries into WEB-INF/lib, like:
servlet.jar, jsp.jar, jstl.jar, and export it into deploy directory of Jboss. I am sure that eclipse-jboss plug-ins, create problem. Sometimes (mostly) it want even to export project I marked to be deployed on JBoss. Is there maybe some other bug-fixed plug in so I can test my application in eclipse, starting JBoss server from eclipse?
The root cause of this issue, which is caused by jar files containing javax.servlet.* in the application's packaging, suddenly showing up prominently in AS-5.1 is this. That fix will be available in the next release of AS. In the mean time, remove the jar file(s) containing javax.servlet.* classes, from your application packaging.