Maybe I haven't copied a million games, but none I've tried so far has posed any resistance. Gun was no exception, it copied to HDD, backup on DVD+R works flawlessly for me. I did notice that the DVD-RW version that I made to test the multi game menu had major problems. I've come to expect this from -RW on some games. Some play fine. Even with those errors, the +R I created from the same ISO worked as it should.
So, it's probably a disc issue IMO. You burned at 8X, you got a new batch of discs, you've changed firmware or burners or one of a hundred other possible problems. I always suggest to anyone that can, start burning bitset +R discs. They work, every single time and DVD-R don't. Even the good stuff.
If that's not an option for you, try burning at 2x. Try another kind of -R or whatever you are using. Unpacking and then recreating the ISO with a new version of craxtion or xiso might work if the issue is not disc related. It's not the game though, backups are totally possible and they work just fine.
GUN is the worst game ever made for the xbox i would throw it away but it worked fine off my HD as long as i had it on there (3 days) no problems at all used qwix to to transfer it...
personally i use Philips 8X DVD-R
Since i can not bitset my DVD's to DVD-Rom that is my best option
they work every time for PS2, Xbox games, and movies.
The choice is your, but -R media is just more compatible with more systems than +R is, that is why everyone has to bitset them so that
they will work right.
I would also suggest burning the 8X discs at 4X.
It does sound like a media issue to me as well, either that or you
did not get all the files transfered when you made the ISO.
