Code 00000071 ERROR : Could not find a source for updated packages

For a while everything looked good. I had installed Sophos Endpoint Security Control on my W2003 Server and successfully protected a number of XP clients. Everything was green on my Dashboard.

Now all of a sudden all of my clients have failed to update. They all have Error Code 00000071 ERROR : could not find a source for updated packages.

If I try and do an "Update Now" from the clients I get a message saying - "Could not contact server".

I've checked my network (i.e. used ping to contact the server, and also checked the SophosUpdate and SophosUpdateManager shares are accessible) and that all looks OK.

Any idea why this has suddenly started happening and what I need to do to get everything working again ? I've tried the obvious rebooting everything in sight but that made no difference.

Thanks

              Peter