??????????//

Sometimes a pokemon game won't work for VBA
(NOT NO$GBA)

Can you offer a better explanation?And use no$gba instead of vba...that's my personal opinion (but they did work for me on my vba when I used it)

which pokemon game was it? what specifically is the problem? the game wont start? or it crashes?it really helps when you give a few details to work with.

You would need to extract it, does it say that the emulator can't support it? If it does then you need to extract.

VBA needs to be updated and modified with a good GBA Bios and some other files in order to run some GBA games correctly, including some of the Pokemon games.Refer to this tutorial.
http://forum.romulation.net/index.php?topic=6326.0Off Topic:
To think of it, it was this tutorial that original lead me to Romulation. I couldn't figure out why the Pokemon games were not working on VBA and everything else was. Googled and found this tutorial and Romulation in the process.