Well, MS wants you to do an in place upgrade, but I got the problem AFTER I did an in-place upgrade (because of a new motherboard). Here's the fix that worked for me: "garethcummings" solution to the same problem on experts-exchange.com http://www.experts-exchange.com/Operating_Systems/Q_20803479.html
Deleting these two keys - HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\PPP\EAP\25
and
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\PPP\EAP\26
did the trick. Read the whole solution, though.
One caveat: it took literally a couple of minutes after I rebooted before the machine responded - it seemed to "freeze", although I still had mouse movement. After this period, though, my previously "lost" connection reappeared, and I didn't have to set up a new connection.
