Ubuntu :: Kpackagekit Was Rejecting (correct!) Password

The problem: when kpackagekit would prompt me to update packages, it would ask for my password. I would enter it, and the dialog would reject it with the message "incorrect password, please try again". Over and over. The password WAS correct -- it worked in Synaptic and on the command line using sudo, and obviously it also worked for logging in.

I suddenly had a hunch that kpackagekit might not be the culprit, and that authentication was being done by a different program -- and lo and behold, the dialog actually said policykit up there...

So, searching for policykit problems out there, I ended up seeing someone reinstalling theirs for their problem (which happened to be different from mine). The code to do that, in the command line:

Code:
sudo apt-get install --reinstall policykit

After that, entering the password after kpackagekit prompts me to has worked fine and the updates happen as nature intended.