CMP relationship fails

[magu]

I succesfully deploy a relationship between 2 tables Street->Blocks. When I try from the client to run getBlocks to retrieve all blocks that belong to a streets I get:
java.lang.reflect.UndeclaredThrowableException
at $Proxy2.getBlocks
...
Caused by:java.io.NotSerializableException:org.jboss.ejb.plugins.cmp.jdbc.bridge.RelationSet

Is this s bug ? a JDBC driver problem or a configuration problem ?

Thanks

[magu]

More info:

It appears that the RelationSet is null as it shows bellow when I catched the exception:

Exception Class: class java.lang.reflect.UndeclaredThrowableException Exception Cause: java.io.NotSerializableException: org.jboss.ejb.plugins.cmp.jdbc.bridge.RelationSet Message: null

Please can someoane help. I did not get any errors when I deployed the beans.

Thanks in advance