The CMP code adds a module dependency on org.jboss.as.cmp if there are any CMP beans in it (via the CMP marker).

If the <ejb-class> refers to a class not in the EJB jar itself, such as in a library jar, this will result in the proxy being created in the EAR classloader and not being able to find JBoss' CmpProxy class.

The solution is to add the dependency to the top-level deployment so it is available in all sub-deployments, rather than the such the ejb subdeployment.