The Mac App Store Is Breaking Apps
Security certificates have expired for many popular Mac App Store apps, preventing them from launching. This issue affects 1Password, Acorn, Byword, DaisyDisk, and Tweetbot, among others. It’s up to Apple to provide a fix, but some users have reported that a reboot solves the problem.
I hit this problem this morning with iBank 5 and 1 Password. I found this: http://apple.stackexchange.com/questions/215332/many-os-x-app-store-apps-are-listed-as-app-is-damaged-and-cant-be-opened,
So far, powering down and back up seems to have worked.
I also have had to enter my Apple credentials after getting an error message that a given app had not been installed on this computer before even though it had. This happened even after the repowering. I assume this is related.
Delicious Library 3 wouldn’t allow me to add an item yesterday because it said it needed a license. I launched the App Store app, and I was signed out. I signed back in, then reinstalled Delicious Library, and it worked.
Tweetbot 1.6.2, running under Mavericks, is dead. Nothing will revive it.
Checkbook Pro from Splasm Software is another one that's affected. Splash is offering free serial numbers for Checkbook Pro from their online store until the problem is resolved.
I experienced problems with both Day One and Mountain. Uninstalling and reinstalling Day One (and resetting all its preferences) fixed that problem, while with Mountain I had to download the app from the developer site and use a free code I was provided to register the product.
I cannot imagine this kind of problem happening a few years ago.
Rebooting did *NOT* fix this problem for me. A few minutes ago MacJournal (mis)informed me that it was damaged and had to be re-downloaded. Instead of falling into that trap again, I logged into the App Store with my credentials, and launched MacJournal from there. All is well (until next time).