The facts:
Upgraded Norton Internet Security 2013 to 2014 without problem on two Windows 8 (64-bit) computers. But on computer number 3, the upgrade results in a broken Internet connection -- unable to connect to the Internet. It generates the Norton errors 8505 and 129 (can't connect to Norton's servers). The peer-to-peer network connections work just fine. This computer, like the others, is connected via ethernet, not wireless. All three desktop computers are configured nearly identically in hardware and software.
Per Norton's instructions, I uninstalled NIS 2014 using the Norton Removal Tool, rebooted, and installed NIS 2013 -- and the Internet connection worked just fine. But upgrading to NIS 2014 again resulted in a dead Internet connection once again.
Even after uninstalling NIS 2014, rebooting, and installing NIS 2014 from the full download from Norton instead of using the Norton Downloader, NIS 2014 killed the Internet connection.
Help! Any idea of what could be causing this behavior? I've built, upgraded, or brought back from the dead about 70 Windows computers, but this problem has me scratching my head. Thanks for what I hope will be the forthcoming help.