Thanks. I am running the following providers (default):
The machine came with Norton Internet Security which I disabled using MSCONFIG (two entries), but I am uncertain if I have gotten rid of all of it. The Windows Vista Security Center shows only avast! running under Malware. I am also running Zone Alarm, and Spybot S&D. ZoneAlarm is shown in the Security Center under Firewall (nothing else). I had suspected Spybot and tested without loading it but got the same result. When I discovered that I could reconnect by stopping avast!, I was running only Zone Alarm and avast! (of the three programs). I stopped Zone Alarm to no avail, and then, when I stopped avast!, I was able to reestablish the connection. Subsequently, after running into the problem, I was able to reconnect by the method described above (disabling and re-enabling avast!) with both Zone Alarm and Spybot S&D running alongside avast!.
I cross-posted this with a post on the thread I started prior to seeing this one as I saw no other way around it.