Cheat Codes and No$GBA v.2.6a

I tried entering codes for megaman battle network 2 on No$GBA, but everytime I do so, it does 1 of 3 things: Displays "?" in check box, Displays "..." in check box, or doesn't allow entry and beeps. What is going on and how can it be fixed? Because I used No$GBA before, but did not have these problems. It was the same version, too.