Thanks for the replies, guys. I can't see how I could have ended up with a used game (Future shop does not sell used games, unless it was a return.. wait.. heyyy) but something that did occur to me, was that though it was bought new, my DS is very old. I got it at the end of 2004, and it is well taken care of, though heavily used. So perhaps something happened with the system that's just the wear of time. I'm going to give Nintendo a call, and see what their take is, I'll update.
Also, thanks for letting me know that it's a bad idea to blow on games. This is something practically everyone does!
Your replies mean a lot, I'm sure you must know how I feel.
Just some more things that might help - This was my first time to the Safari Zone, with the missions completed. Also, that day, I tried the Pokeathlon for the first time. I have all sixteen badges, but this was my first time catching generation III and IV Pokemon. I don't know if all these new things overloaded the system? Then again, why would they be programmed in if that was possible? I'm just grasping at straws..