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.