You should try going to their site and download from there. They have a nice log on screen that only asks you your name and e-mail account:
http://www.marsware.net/accounts.php
Hope this works for you!
edit:
After posting I realized I bought this program directly through marsware's site.
I'd still hope it would work though. It even posts the key right on their site after you log it. I've redownloaded the program several times and never needed my key.