Error during download: “Error 403 forbidden” when updating apps from App Store in OS X

I’m using a MacBook Air with OS X 10.6.

I’m not able to update or download any apps from the App Store anymore.
I tried to solve it this way but can’t make it work:

Mac OS X 10.5: Web Sharing – “Forbidden 403” message appears instead of website content

How can I fix this?

I signed out of icloud account, went to itunes preferences: advanced tab, reset warnings, and reset cache. then restarted the computer. It worked for me. Hope this helps.