Well, I doubt that the internet connection is the problem. I ahve two PC's here. One Vista and one XP, with both legitimate copies of COD4, so two different key codes. I use one (AlphaW0lf) for playing and one (WatchDog) for speccing for campers. The WatchDog / XP machine i giving me the problem with 90042. The Vista machine is still working fine.
On the XP machine I use AVG as AV, on the Vista I use NOD32. I shut down ALL AVG-processes, but to no good. Like I already mentioned, I didnt install any programs in these few hours, an thougt I had the solution by setting a restore point of a few days ago: no good. Going to fill in a form right now.