They don't tell us much more than we already know, which is there is a bug in the Hallmark app. This presumably doesn't affect everybody using but something on your machine is provoking it. The usual suspects are corrupted preferences , corrupted fonts or an application that's been installed with incorrect permissions. Since you have already sought advice from Hallmark they should already told you how to clean out the preferences and reinstall the app.
I assume that the app comes with a lot of clipart, etc. that you put together to make a card. It's possible that one of these graphics is corrupt. Perhaps you are the only person who's used it on a Mac. You might try starting with a blank card and do something very simple. If this works, try adding a graphic, build up to see if you can narrow down the cause.
Or, you could ask Hallmark to refund the cost of the app and use another service for creating your card. There are plenty of companies in the market.
C.