Starting on November 11th 2015, Mac App Store customers began reporting that App-Store-distributed versions of Coda fail to launch. This is not a Coda-specific problem, it affects every app in the App Store.
The root of the problem seems to be that the certificate used in Apple’s App Store receipts has expired. We’re confident Apple is aware of the problem, and will be correcting it as soon as possible.
In the meantime, when you launch an App Store copy of Coda (or any other app distributed in the App Store), you’ll see a dialog asking for your Apple ID password. In some cases, it will be able to download a new receipt and fix the problem. Hooray!
In other cases, for reasons we do not yet understand, the new receipt fails, and the app bundle is corrupted. In this case, you will see a message like:
"Coda" is damaged and can't be opened. Delete "Coda" and download it again from the App Store.
Indeed, for some users, deleting and re-downloading Coda from the App Store will fix this problem. Hooray!
In other cases, you will need to restart your Mac and try again. For some users, in some cases, there is currently no resolution.