I know it has been a while since you started this topic but just in case you are still interesting try the suggestions below.
Did you try to build your EJB project using the libraries of Jboss 6 instead of 4?If no, try to do this.
Then, remove this import (if you have)
import javax.annotation.EJB (to be removed)
and replace it with this one
import javax.ejb.EJB;
(check also the link http://community.jboss.org/thread/167455)
Also, build your project using jdk 1.6.
After doing this, then it should work.
Hope this helps.
Good luck