I've tried continually turning off the power and retrying it, to no avail. Broncoeman said something about bit rot...could this be it?
I also wanted to say that the man I purchased the cartridge from has refunded my money, and doesn't require my returning the game, which is very nice. Everything worked out.
Meanwhile, I'm going to try different methods of cleaning, perhaps a light abrasive method, perhaps I'll open the cartridge, I dunno. I can't give up yet . Thanks everyone who offered advice!
--Brandi~