US v4 with Neo 2.5 DVD key

I have a US v4 (30001R version 4) with a Neo 2.5 installed. I am using a gameshark v1.9 (I think since it has a 1.9 sticker on the back). I've yet to get the GS to work. When I use the GS, the PS2 just goes to the "Please insert a playstation or Playstation 2 format disc." screen. Is this a problem with the GS or the chip? It does this if I use the cdr boot modes (1 & 2) of the Neo 2.5 and also in original mode (chip off).