Environment: HP-UX 11i, Weblogic 8.1 SP1.

We're getting the following error when we start managed servers in our clustered environment: due to: java.net.SocketException: Can't assign requested address.
java.net.SocketException: Can't assign requested address
at java.net.PlainDatagramSocketImpl.join(Native Method)
at java.net.PlainDatagramSocketImpl.join(PlainDatagra mSocketImpl.java:134)
at java.net.MulticastSocket.joinGroup(MulticastSocket .java:274)
at weblogic.cluster.FragmentSocket.initializeMulticas tSocket(FragmentSocket.java:92)
at weblogic.cluster.FragmentSocket.start(FragmentSock et.java:109)
at weblogic.cluster.MulticastManager.startListening(M ulticastManager.java:164)
at weblogic.cluster.ClusterCommunicationService.initi alize(ClusterCommunicationService.java:52)
at weblogic.t3.srvr.T3Srvr.initializeHere(T3Srvr.java :922)
at weblogic.t3.srvr.T3Srvr.initialize(T3Srvr.java:664 )
at weblogic.t3.srvr.T3Srvr.run(T3Srvr.java:342)
at weblogic.Server.main(Server.java:32)

We also get the same error when we try the util.multicastTest application. So far, we've done the following things to troubleshoot this:
1) Different multicast addresses/ports;
2) The util.multicastTest app.
3) We're researching whether or machine or network may be causing this, but since the admin. server and managed servers are running on the same server, I don't see how the network could be causing this.

Can anyone give me any ideas as to what might be going wrong? We've set this up on other machines before with the same OS and same version of Weblogic. So I'm at a loss at the moment as to what might be going wrong.

Thanks in advance for any help...