Action Replay, Code Breaker or GameShark?
 

I've got a chipped PS2 (Magic 3 I believe) and am having a little trouble with booting PS2 backups. I've burned a Sega Genesis emulator PS2 CD and SNES emulator PS2 CD that both boot perfectly. I also have one PS2 CD-ROM game that I used the CloneCD "PSX LibCrypt" profile to burn a backup of. That also booted perfectly. However I have this other backup that I made a while before I got the PSX LibCrypt thing and can't get it to boot. I've heard that you can use a GameShark or whatever to boot backups in conjunction with a no-solder mod. Would it also work in conjunction with a regular mod chip? If so, which should I use: GameShark, Action Replay 2, or Code Breaker?

I doubt your bad backup is going to work with any Cheat Code CD if it does not boot with magic 3.1, unless you have a PAR code to remove libcrypt protection. Even if your bad backup was protected with libcrypt it should have booted a little bit. These must be PAL games right? Does it try to boot with the Playstation 2 logo or does the laser click and go right to Red screen?

They're NTSC games. The one that won't boot goes to the red screen.

Libcrypt is not your problem. Probably a bad burn.