Clients cannot get new router certificate.

Hello,

We have a number of client PCs (Both Windows and OS X) that are showing up as offline in SEC.  Looking at the RMS log, they all show the same thing:

06.09.2011 12:17:21 92C0 I SOF: /Library/Logs/SophosMessageRouter/Router-20110906-021721.log
06.09.2011 12:17:21 92C0 I Sophos Messaging Router 3.0.13.1747 starting...
06.09.2011 12:17:21 92C0 I Setting ACE_FD_SETSIZE to 138
06.09.2011 12:17:21 92C0 I Initializing CORBA...
06.09.2011 12:17:22 92C0 I Setting connection cache limit to 10
06.09.2011 12:17:22 92C0 I Creating ORB runner with 4 threads
06.09.2011 12:17:22 92C0 I Getting parent router IOR from [SERVER IP]:8192
06.09.2011 12:17:22 92C0 I This computer is part of the workgroup WORKGROUP
06.09.2011 12:17:22 92C0 I Getting a new router certificate...
06.09.2011 12:27:22 92C0 I Timed out, resending certification message...
06.09.2011 12:37:23 92C0 I Timed out, resending certification message...
06.09.2011 12:47:24 92C0 I Timed out, resending certification message...

etc 

Most of my testing has been done on OS X, but it both Windows and OS X show the same symptoms and reinstalling sophos on the client doesn't fix the problem.

On the server, the following entries appear in the RMS log:

06.09.2011 11:50:36 0460 I Routing to CM: id=00657C6C, origin=Router$[SERVER NAME].Router$[CLIENT NAME]:0, dest=CM, type=Certification.UniqueTokenRequest

06.09.2011 11:51:41 14D8 W Delivery failed(Timeout) for message type Certification.UniqueTokenRequest, originator Router$[SERVER NAME].Router$[CLIENT NAME]:0

These messages seem to appear every time the client resends the certification message.

I don't think the problem is network related as the server seems to receive the request, and we have plenty of computers on the same client subnets that can communicate fine.  I have tried disabling the firewalls on both client and server to see if that may be the problem, but there was no change.

I'm hoping someone here can point me in the right direction, so far I haven't had anyone with the same problem.

Please let me know if I have left out any information.

Thanks,

Tristan.