Description of problem:

Quite regularly (a few times per day), a new window pops up on my GNOME 3 desktop
titled "Software Updates". It contains the text:

  Could not get updates.
  Failed to process request.

When i press 'More details' it shows:

  Operation was cancelled.


Version-Release number of selected component (if applicable):

Fedora 18 beta.

How reproducible:

I don't know how to trigger it 'on demand' -- it simply occurs regularly.
  
Actual results:

See above.

Expected results:

Either the update should simply work -- or I should see an error message which contains more useful information. In particular: how to solve the problem.

Additional info:

I tried 'yum update' in the terminal and it worked like a charm.