My Mac App Store had developed a strange problem: it couldn’t remember that I had installed any of the programs.  Thus, it would show the list of all purchases from the store along with the active button that says “Install”, not the button that says “Installed”.

Also, it wouldn’t show updates for any of my installed programs.

I could install any of the programs again — that would work.  But almost immediately it forgot that I had installed it.  It was like Dory from Finding Nemo.

I tried a lot of things to fix it.  I rebuilt the spotlight index.  I repaired permissions.  I rebooted into safe mode.  Nothing helped.

I started looking into the Mac console, and started eliminating (as best I could) the errors that kept appearing in the list.

Finally, the error that fixed it was one that said:

1/23/13 3:38:53.941 PM sandboxd [9668]: ([9666]) mdworker(9666) deny mach-lookup com.apple.ls.boxd

Fixing that problem returned my MAS to normal usage.  How did I fix it?  Via this post on someone’s blog:

Fixing sandboxd: mdworker deny mach-lookup com.apple.ls.boxd error in OSX 10.8.2 (and other versions)

Specifically, the part (click on alternative solution) that reads:

You can completely fix all the mdworker related sandbox errors in Console (including the ‘cannot talk to lsboxd’) by editing the system.sb profile rather than the mdworker ones. The system.sb file is used by all Apple system processes that run under the sandbox, including mdworker. If you modify this file (which is located in /System/Library/Sandbox/Profiles) to include: 

(allow mach-lookup (global-name “com.apple.ls.boxd”))

(allow mach-lookup (local-name “com.apple.ls.boxd”))

That was all I had to do.  In doing my searching (and I searched long and far), I saw a few other people who had this problem.  I hope by tying the solution to the symptom (as the blog post I found didn’t mention the Mac AppStore at all) in this post someone else will find the answer quicker than I did.