Hmm.. I searched for your problem and got the following at versiontracker.com:
[quote]Definitely better than anything else available (except of course a real GBA). Some games simply do not work (Pokemon Advance, Yoshi's Island) and some only work with a real BIOS file (put loose in same folder as Boycott application). Right now enjoying Kirby Advance, Metroid, Castlevania II… [/quote]
Maybe that's related... And if you have an Intel mac then maybe you could try CrossOver/Darwine to see if a windows emulator works...