Well, on most disks, there is an audio track. When you put it in a CD player, it will play the track telling you to stop playing because it might damage your system, you, the nextdoor neighbors, make you crazy and kill somebody or make love to trees in that order.
I haven't seen many games (if any at all) on the PSX that uses such a warning track. Probably because the first track on PSX games should always be a data track, which makes it kinda pointless to have the warning on track 2, when chances are that the "possible" damage is already done ;p
Considering that audio track is the typical 3 minute dummy (Psx's isn't supposed to be able to read it, infact most games use this trick), you can recompile the ISO without it and there won't be any issue.
I've fiddled with many PSX games, some even works if I just toss the files together and burn as a mode 2/XA CD on the fly, without using any tools to create an ISO first with region/license info and such.
But Capcom games seems to hate being touched (even after I've manually recreated original LBA layout without even changing any files).
I just wonder if there's something I've not thought of or something. Most likely, my mistakes are related to the last dummy file on the disc, which has the same starting point as the audio track, making the zdata be a mixture of a file on the disc and the blank audio track.