"We could not complete your App Store request"
Since a few weeks App Store runs into the same errors after every start. See the Screen shots.
The first error after the start says "One moment please. Connecting to the iTunes Store. Loading ...". Then nothing happens. When I click to the "Updates" or any other button the second error message appears: "We could not complete your App Store request. The App Store is temporarily unavailable".
I switched off the firewall and virus scanner but w/o effect.
When I log in to another user App Store works as expected and starts normaly.
How can this error be fixed?
Thanks and best regards.
MacBook Pro (15-inch, Mid 2012), OS X Mountain Lion (10.8.2)