Thanks for suggestion 'jkgvnr' - I had tried all this, even had PTC support stuck for a while. The problem appeared to be licence related, but we couldn't see why.
My big problem was McAfee (Internet security suite which includes firewall etc.) : uninstalled McAfee, uninstalled PrOe stuff, then did clean re-install of ProE stuff - result, but I now need to review my security provisions.