Can't log in to Apple store; 'plist parsing error' after STATUS_CODE_ERROR

Two week old 15" MacBook Pro. I had two updates this morning, xCode command line tools and iMovie.

The xCode command line tools installed and restarted the laptop.

After that, I couldn't log in to the Apple Store to install iMovie; I got a STATUS_CODE_ERROR in the lower left hand of the login dialog.

I quit the App Store app, then restarted it, and tried to install iMovie again.

I still couldn't log in to the Apple Store to install iMovie; I got a plist parsing error in the lower left hand of the login dialog.

There is an Apple Support Communities string for STATUS_CODE_ERROR that has 1800+ entries, seems to be global.