Opening/Saving Old Version Files?

I used to be very active in the card creation community, and just recently started designing cards again.  First step was to download the current version of this excellent program.  I was very excited to be able to pull in my old cards (well over 3000) just fine, including the art I had associated, etc, but if I make changes and save (or just save in general), I get a MinGW Runtime Assertion error (Assertion failed!), and the program crashes. Can anyone tell me how I can fix this? It saves new files just fine, but I'm going to cry if I have to re-enter all 3000 cards into a new file. T_T