[escobar]

This happened to me a number of times over the last few days. The first time it happened I shrugged and rebooted the computer. When it came back up, it asked me to authentcate with the MAS and those few apps worked. Then, later that night, the same issue happened with a different app. I actually uninstalled and reinstalled the app and that worked.

Hopefully they've actually fixed this now but I was pretty confused about what could be going on. The only other time I've gotten messages like that is when I'm opening an unsigned application Apple doesn't think is good, and the Security settings say to only allow trusted software.

[eridius]

There seems to be a bug in the system where sometimes it reports an app as damaged when it's perfectly capable of downloading a new receipt (this is why a reboot works, because the bug seems to only crop up after some period of usage). When I bought a new iMac and transferred all my stuff from my old computer, I had this exact same issue, all of my MAS apps were reported as damaged. After reinstalling one, I tried rebooting, and that worked; got a password prompt for the next MAS app, and the rest just worked fine at that point.

Hopefully they're aware of what's causing this bug and will fix it in an OS update.

Of course, when the certificate is actually expired, and they haven't replaced it yet, then the "damaged" dialog is reasonable, because the system cannot get a valid replacement receipt. But once they replaced it, OS X should have just started working again. In fact, I'm going to go file a radar right now.