I dont have the game myself but a 2 second google lead me to this:
Tony Hawk Proving Grounds
WORKS YES
PAL
Game loads however after starting up single player disc cannot be read error appears
I presume this was for the back up loader 0.3g thread about a trillion years ago, so I have no idea if its been fixed or even looked into on neogamma.
Try forcing region (depends on the region of your backup) or you could always try patch the iso to 249?