Hi All,
The problem turned out to be the fact that there were no hostnames for the primary domain, when I tried to add them in server-manager it would not allow me to activate them! So I reconfigured the server with a different primary domain name, checked that all the hostnames were there, they were, then I reconfigured the server again using the old primary domain name and then checked the hostnames and they were all OK! So the bottom line is I don't know why the hostnames would disappear but it is working OK again.
Del