Can you share your pom.xml and web.xml with us? You can also take a look at our tutorial project. I will automatically start JBoss in dev mode (all you need to do is mvn gwt:run):
In your web.xml try getting rid of the resource reference to ErraiService. We removed this from Errai 2.4.2.Final so it could be causing your problem, or at best it's not doing anything useful. You can also get rid of the BeanManager reference too, as it is not necessary when deploying to Jboss AS.