Problems with apps from the Mac App Store?

Recently, Apple sent all developers this email, which contains helpful information in case you suddenly experience problems with applications obtained from the Mac App Store:

As a reminder, the Apple Worldwide Developer Relations Certification Authority Intermediate Certificate expires on February 14, 2016 […].

[…], we want to make you aware of potential issues your users may encounter due to the renewed certificate. Users running OS X El Capitan (v10.11 or v10.11.1) may receive a notification that your Mac app is damaged if it utilizes receipt validation to request a new receipt from Apple. They can resolve this issue by restarting their Mac or updating to OS X El Capitan (v10.11.2). Mac App Store customers running OS X Snow Leopard (v10.6.8) will be unable to purchase new apps or run previously purchased apps that utilize receipt validation until they install the Mac App Store Update for OS X Snow Leopard, which will soon be available via OS X Software Update.

TabView and Tablatures on Mountain Lion

People are reporting that MIDI playback doesn’t work since they updated their system to Mountain Lion.

It appears to be due to a strange conflict between HIDRemote (the code used to support the Apple Remote) and Mountain Lion’s sandbox (which restricts what applications can do). Actually, it seems that sandboxed apps have no way to support the Apple Remote right now.

A new version of both apps has already been submitted to the Mac App Store, quite some time ago. They are currently being reviewed by Apple and will be available as soon as they publish them.

UPDATE: this appears to be worse than that, it looks like it’s an actual bug in Mountain Lion that affects sandboxed applications (ie. everything you might find on the Mac App Store). I’m getting in touch with Apple’s engineers to see if there’s a way to workaround it, or if the only thing to do is to wait for a new 10.8.x release (10.8.1 doesn’t fix it).