Iam using weblogic 9.1 hibernate3.0 and spring 2.0
Everthing works when we are on single server ..., in the cluster environment we are getting java.rmi.UnmarshalException: failed to unmarshal interface java.util.Set; nested exception is:
java.lang.ClassNotFoundException: Failed to load class com.abc.aaa.CCC
Iam not sure its something related with the hibernate or not ....
has any one encountered such kind of issues ...?

ClassNotFound?

Could it be a simple as the libraries linking the jar files are not available on both sides of the connection. That's what marshalling is

Seems like you're obfuscating your code. If you are, both sides of the network need the same set of obfuscates Java files, otherwise the names of the classes won't be consistent.

Try it without obfuscated Java files in a non-deployed, sandbox environment first.