First of all, hello and welcome to Driver Madness. DriverX.
It seems that you read my other post
here. but just to confirm have you turned UMD Cache off.
Turn on the PSP with no game inserted. Go to
Settings --> System Settings --> UMD Cache --> Off
You said you used turned off USB cache, I just wanted to make sure you turned off the correct setting.
Where did you download this game from? I was unaware that it was downloadable. (Could you have download the first Driver title, Driver: You are the Wheelman from the playstation store)
Some other information we will need to help target the problem is some information about your PSP.
On the right side of the box you got your PSP in there will be a little sticker it says something similar to PSP-2002 PB but may be different. What model PSP are you using at the moment?
If you not sure, when did you purchase the PSP?
This may help me determine the model of your PSP.
Good Luck,
and I hope we can get Driver running on your PSP.