Calling an EJB from Java Mappings in PI 7.1

In my operation mapping, I am using a Java class which in turn invokes an EJB using JNDI lookup.

When I execute the code, the class is successfully finding the EJB using JNDI, but invoking it I am getting a java.lang.NoClassDefFoundError.

If, I add the class it cannot find to the jar containing the Java mapping class, I get a java.lang.ClassCastException.

Has anyone been able to call a custom EJB from with a Java Mapping class?

Any help appreciated.

Thanks.