More Sonic CD Problems

I've checked through previous threads and followed the advice given, I think I'm nearly there, I have various versions of the game, beta, jap, us, pal, all seem complete and correctly titled. It's when I try to run the game in kega it asks me for the bios. I've selected what I think is the correct file in the sega cd tab, it just doesn't run.

What are you selecting? Make sure the bios are the same region as the game.

yep. checked that.

Directory linked?

I put the BIOs in a folder, named 'BIOs' then I configure the bios, if i run it again and it says 'check bios' i just re-do it and it plays fine