You'll find that it's a software & hardware issue. Just got to ask if your game is a copy?

There has been reports of the disc freezing up in the game on several GH forums and sometimes the case is to clean the DVD lens with a disc cleaner. Others have tried turning the PS2 console from the horizontal position to the vertical one (vice versa).

The quick term solution given is to restart the track or in some cases the entire game. I've encountered this about 5 times since getting a pre-release of the game and since moving the PS2 into the horizontal position I've had no problems since (keeping in mind my PS2 is the original 1st day release & is over 5 years old & still ticking)

Hope this enlightens you a bit more & have fun shredding those tunes