Pokemon Crystal Visual Boy Advance GameShark codes not working on MAC?

I can't get the codes to work for Pokemon Crystal on my Visual Boy Advance, and I'm running VBA on my MAC. Any help would be appreciated! I put the GameShark code into the VBA but when I load Crystal, nothing's different. I would like 99 Rare Candies so if you could post the solution to my problem and that code as an example that would be nice.