OK. I am using JBoss AS 6.1. "EAP 6" is build over JBoss AS 7...
There were errors in my Remote interface JBoss 6.1 does not report properly where JBoss AS 7.1 did.
So now my EJB3 deploys in JBoss AS 7.1
But I still completely obscure "error due to the following reason(s): java.lang.ClassNotFoundException: Null class name" in JBoss AS 6.1