Starting 14th of February, hundreds of thousands of Mac users round the world will suddenly find that most, if not all, of their Mac App Store apps previously downloaded have suddenly become damaged. These apps won’t launch anymore either, and this will include 2Do.
This is a known bug on the Mac
that Apple has now fixed. However, the fix may or may not work for you. Their recommendation is:
1) Try and reboot your Mac. If that doesn’t help:
2) Delete the app and download again from the App Store. Your data won’t be lost, simple drop 2Do.app from under Applications onto the Trash and empty it. Now download it again from the App Store.
On behalf of Apple, we sincerely apologize for the inconvenience caused.
If, after the above, you are unable to sync
Given the certificates expired, the app may refuse to sync with the previously stored state in the keychain. The following should help in case you have already synced your data to the cloud:
2. Install it again by downloading it from the App Store
3. Setup sync from Under Preferences > Sync
4. When prompted, select Replace Local Data