Java Relection / RMI Exception is Baffling Me

Do any of you java gurus know what root cause is likely responsible for the following exception?

This exception only began occurring after a JRE upgrade (now using Java SE 7 [1.7.0_67]).

Caused by: java.lang.NoClassDefFoundError: Could not initialize class com.sun.proxy.$Proxy0
at sun.reflect.GeneratedSerializationConstructorAccessor2.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at java.io.ObjectStreamClass.newInstance(ObjectStreamClass.java:967)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1782)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1350)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
at sun.rmi.registry.RegistryImpl_Skel.dispatch(Unknown Source)
at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:409)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:267)
at sun.rmi.transport.Transport$1.run(Transport.java:177)
at sun.rmi.transport.Transport$1.run(Transport.java:174)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:556)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:811)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:670)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)