102 is not an error code and its probably nothing to do with DNS as the message came from a server. The fact that is sometimes works makes me think that it is either;
1) software on your machine messing with the browser’s proxy settings, or
2) virginmedia’s proxy servers (they will have transparent ones you can’t avoid)
3) web browser (try using another one or re-installing this one)
trying a different browser will show if its your briowser or PC. If its 1 its probably spyware or spyware monitoring software. If its 2 you will have to pay for an SSL proxy service otherwise all http traffic will go through virgin’s proxy servers anyway.