hello,
I don't own a GBA, but a Nintendo DS. I have an EMS 64 card for my DMG, and I see it should fit in a GBA. The Nintendo DS can use GBA cards, yet, the EMS card doesn't fit in the DS (it's the same size, but there are marks in the DS which make sure you can't insert original GB carts into it. So is the EMS really compatible with GBA? Now I'm thinking they didn't make the marks in the GBA support but they made in the GBA cards (and the same in the DS), that would explain something...