Error messages when trying to open Easy Envelopes: data not in the correct format

When attempting to open an my Easy Envelopes app that I've had for over a year I got a message that I needed to sign in to Apple because the App Store thinks the computer I'm using is not the computer I purchased the app on. It is the same computer. Then I tried to sign in like it asked , but I got an error message saying "date couldn't be read because it isn't in the correct format". What's going on here? I did not upgrade anything. Is it just a new year thing? I've attached some screenshots.

[Edited by Moderator]