Nevermind, i found my error. Thanks for your interest anyway :)
Putzeudel, it would help others that run into similar issues if you would provide some details on what the problem was and how you fixed it.
I had the same Error..
On my jbossesb-server-4.5.GA, dir /jbossesb-server-4.5.GA/server/default/lib/ I paste these jars:
jboss-annotations-ejb3.jar
jboss-aop-jdk50.jar
jboss-aspect-library-jdk50.jar
jboss-ejb3.jar
I take these files of my jboss-4.2.2.GA. Now my EJBProcessor works fine.
I don't know why it doesn't work just with the jboss-ejb3-client.jar.