The exception message coming from ensureObj() is somewhat confusing, it should be something like

Cannot get java.lang.Long field com.test.ProductBean$ID.productID from instance of type com.test.ProductBean$ID

as the field.getDeclaringClass() == com.test.ProductBean$ID.class is not the same as the class of the passed instance == com.test.ProductBean$ID.class

Smells like class-loading issue up the stack.

Steve Nakhla, can you reproduce this in a test case without the application server?