No, event 4226 is only a notification that tells you that you attempted to open more then 10 connections at the same time. The network administrators job is to determine if that was something normal (such as bittorrent downloading) or something malicious (such as a WORM or Virus).
I suspect that your problem is with your router, or perhaps your modem. If they are the same as before you installed sp3, then your experiencing something I've never come across.
I guess its possible you have a problem or incompatibility issue with your system, or perhaps a bug in windows sp3, but my feeling is its a router problem. Have you tried rebooting your router to see if your connection is restored?
The method your using to restore the connection could (possibly) signal the router of a new connection, making it restart itself. This is just a theory to explain how it could be a router problem, but to be honest, I have no idea where the fault lies...
If it is your router, try a firmware update, or last resort, limit the max connections in BitComet.
Also, if you use a 3rd party network management software program, I'd recommend uninstalling it. I know the ones made by Nvidia (NAM) are horrible and can cause this problem.