Still have the problem, even after a reboot. I'm not sure what update broke this, but I think I'll have to do a System Restore back a couple of days.

Slartybart,

Tried that and still have the same issue.

Ah, thanks. I didn't realize it was there as well.

Just to be sure, you opened the start menu, searched for Command Prompt then right clicked it and said to Run As Administrator?
The title bar should say "Administrator: Command Prompt".

You get that error when you don't run the Command Prompt as Administrator.

But, I ran the command successfully and still have a non-working Store app.