This was caused, for me, by Norton Internet Security. I have had lots of network problems be caused by firewalls in the past, but I didn’t even know Symantec was running on this computer because its icon didn’t appear in the taskbar. This is a frequent problem on Windows XP, but this is Windows Vista Home Basic. Still the same problem here. Even if it looks like Norton isn’t running, check anyway. Run it from the Start menu. To disable the firewall:

1. Click the Norton Internet Security tab.
2. Click the Settings section.
3. Click Internet Security and Firewall Options.
4. Go to General Settings under Personal Firewall.
5. Turn Firewall Protection Off, and click OK.