Cannot Install or Update Apps in App Store - Error 13 I can currently no longer update or purchase software in the Mac App Store.

I have cleared Safari's cookie cache, cleared ~\Library\Caches\com.apple.appstore logged in and out again, but none of these help.

The error message is:



We could not complete your request. There was an error in the App Store. Please try again later. (13).

Anyone else experienced this? Any fixes?

In the console I am seeing:

17/08/2011 15:30:15.384 com.apple.SecurityServer: Failed to authorize 
right 'system.install.software' by client 
'/System/Library/PrivateFrameworks/PackageKit.framework/Versions/A/Resources/installd'     

[6043] for authorization created by '/Applications/App Store.app' [9337]


Update: I logged in as admin and the App Store works fine. So some sort of Prefs file is hosed in my main user. Does anyone know which one it would be?
I seem to have fixed the problem.

I used opensnoop to follow all file accesses while the app store was running. 
I spotted that
~/Library/Cookies/com.apple.appstore.plist
was being accessed - this file had not been deleted by Safari when I cleared all cookies!
The file had incorrect permissions - I deleted it.
Now the App Store seems to be working again.

Opensnoop is a great tool!