Never mind, I think I figured it out. I didn't encrypt the YSMenu.nds file properly. This thread helped me out too: http://gbatemp.net/index.php?showtopic=103879&st=0
This does not seem to be working with YSMenu0810211800.zip. I followed the instructions exactly, but I'm getting an error on the DS as follows:
Or maybe I did something wrong? Please help. Thanks!