GS2 CD does not work.

[Beefcake]

I bought a gameshark off of a friend of mine and it doesn't work in my PS2. The PSX CD works fine, but the PS2 CD doesn't boot. It's not a backup and it worked on his system. He used the NEO USB mod chip and I'm using the solderless. I have a version 4 PS2 and the GS2 is version 1.6. Does anyone have a possible explanation as to why it doesn't work???

Thanks in advance.