I have the same problem. I'm moving a project which did run on JBoss 4.2.2 to JBoss 7.0.2. Web.
With JBoss 4 it was possible to reference an EJB-Class without packaging the EJB-JAR into the Web-App. With JBoss 7 this doesn't seam to work.
My solution is to add the exported EJB-JAR to the WEB-INF/lib folder. The EJB isn't deployed alone but with the WAR-File. Isn't it possible the deploy them seperately without running into the ClassNotFoundException?