game works on friend's dc but not on mine

[Trunks]

my friend has just burned crazy taxi 2 and grandia 2 disc 2 for me. we tried the games at his house on his DC, and they worked fine. But when i got home, i put them into my DC, the DC didn't run it, it thought it was an audio CD. my friend's DC is newer. he previously burnt grandia 2 disc 1 for me, and it worked perfectly. any idea's? the disc 1 was burnt at 1x and cdrom, but disc 2 and crazy taxi 2 was burnt at 4x and as an audio cd. they are all self boot.