Ok, I've played other games straight from my disks, and a few ISOs, but this one is giving me an error.
"CDVD Plugin Failed To Open. Your Computer may have insufficient resources, or incompatible hardware/drivers.
Press Ok to go to the Plugin Configuration Panel."
I even tested another game out to seeif it was a problem since I restarted my computer, and others work fine. I'm using the 0.9.7 beta.

Just unload the iso from any virtual drive (like daemon, alcohol, etc) and select it from the Browse feature in CDVD -> Iso Selector

Once it's selected click the Boot CDVD (fast) and play the game...

If running an ISO file: Dismount the ISO from any program like daemon tools etc. Then CDVD->Choose ISO, then ISO selector->Browse, find your ISO and System->Boot CD/DVD (fast)
If running from DVD disc: Config->Plugin/BIOS selector->On CDVD choose Gigaherz CDVD->Configure it and choose your proper DVDrom drive letter and finally System->Boot CD/DVD (fast)

If it still fails, remake the ISO using imgburn

It's not mounted to anything, I've chose it in the browse selection, and hit both full and fast, same thing. anything else?

Tell us which is that "this one" game, it may help

lol, ok. Kingdom Hearts 2 Final Mix. I've played KH1 and KH2 no problem,(other than slow parts, probably from disk read or processing) but this one is, do I have to do something special? I've seen others play it...

Try remaking the ISO from your game disc again with ImgBurn.

ok, I tried moving it, to my other hdd, and load it from there, to make sure it wasn't "in use" or anything, and I got it to work, although it wasn'tbeing use or anything to begin with. but I listened to what you said about making sure it wasn't mounted or anything, and did a double check. thank you for the help guys, it's working now.