After running the fix I described in a previous message, my AppStore stopped working again.
Browsing through this forum didn't help at all, but I finally found this post by Joseph Scott:
Finally a solution that actually solved the problem!!
- Shut down your Mac.
- Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
- Turn on the computer.
- Press and hold the Command-Option-P-R keys before the gray screen appears.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
Thank you, Joseph
Note: when started again, AppStore shows app updates are available, even though I updated the apps minutes ago. I'll try to find a solution for this problem, but at least now I can browse the AppStore and install apps.
AppStore also stopped working for me after upgrading to Mavericks, but I was finally able to get the thing working by partially doing what uptimistik suggested in another topic in this forum.
Open up Terminal and type:
sudo rm ~/Library/Preferences/com.apple.appstore.plist
sudo rm ~/Library/Preferences/com.apple.storeagent.plist
(this will ask for your password).
I also have Little Snitch installed, so I allowed all connections to the AppStore application and storeagentprocess. The developers of Little Snitch did define rules to allow these to apps to connect to *.apple.com, but Apple must have changed something with Mavericks.
After that I did a restart, and the AppStore is working again.
Hope this helps