App "Can't Be Opened" Error
Opening one of our applications may result in the error message:
[App Name] can't be opened because it was not downloaded from the Mac App Store.
This means that your Mac's Gate Keeper settings forbid opening apps from other sources. To change this:
1) Pick "System Preferences" from the Apple menu at the top of the screen.
2) Click the "Security & Privacy" pref panel, and then "General".
3) Click the lock in the bottom corner to make changes, and enter your Mac's admin password when prompted.
4) You should see options for what apps can be opened. Pick the middle option, "App Store and identified developers".