A recent receipt validation problem has caused some Mac App Store apps to display this error message when launched, and Paprika is one of the apps affected by this problem:
To resolve the problem, please follow the instructions as advised to delete Paprika Recipe Manager from your Applications folder, and then reinstall it via the Mac App Store.
You will need to make sure you are logged into the Mac App Store using the account originally used to purchase it.
Also, you may need to empty your Trash and restart the Mac App Store for it to pick up that Paprika has been deleted.
Finally, your data is stored separately from the application file, so you can safely delete and reinstall the application without worrying about data loss.