Testing multicast connectivity (example tool: http://download.oracle.com/otn/java/coherence/coherence-331.zip) results in one of the nodes successfully receiving multicast messages, while the other(s) fail to.
Setting the multicast group address between 188.8.131.52 and 184.108.40.206 will make the connectivity work, but addresses outside this range fail to work.
Some routers/network elements filter globally-scoped multicast addresses, but let the reserved range through.
Use the reserved range, however this may be more polluted in various networks or not available. Please contact your network administrators on picking the range.
Allow multicast traffic on the desired range/address, contact your network administrators.