Ok, so this morning I decided to give it one more try and deleted the game and redownloaded it, and it now seems to be working fine. Sorry to waste your time.
I can't imagine what the issue could have been... With the first game version I couldn't even get to the save screen, it just immediately threw up that error page. Then the second one I tried would get as far as the save page, but have the error when I tried to actually save it. I dunno, maybe my laptop was having a little quirk.
Anyway, it's working fine now. Thank you for trying to help!