Hi Riccardo,
Upgrading the OS and UFM is something I recommend you doing anyhow (not just for testing. Should you choose to stay with RHEL5 this might be a problem with future upgrades going forward. Besides, the newer versions of UFM gets only better and better...
As for your Java, not sure whether i can specify any specific error. All kind of Function not supported variations are included. Get your Java from https://www.java.com/en/download/ - This is the ONLY java i know working for this product.