Thanks - that's a useful link. I can see that DNS cache could add an additional dimension to the problem if NTL were having one of their frequent DNS problems. Under those circumstances it would presumably be a good idea to reduce the default value for the TTL time for negative responses from 5 minutes to nothing in order to force the PC to have another go at getting the right answer out of NTL's DNS servers. Maybe you could argue that it should be done for positive responses as well - which, come to think of it, is what you effectively did by stopping the cache service.
Mike