FIXED.

I tried the advice at this post:
http://www.microsoft.com/communities...e92&sloc=en-us

And it turns out that my active network adaptor was indeed missing Client
for Microsoft Networks, and installing that, then rebooting, solved my
problem.

Wow. I am so tired. I would be happier if I wasn't so frustrated and tired
from all this.
To Microsoft tech people: please use this info to bring to light the cause,
and cure of this problem, so that others like me can have their problem
solved with a nice easy support page