I had the same problem.
I couldnt load games (original or backup) from disk channel... However no problem using gamma channel.
I had preloader instaled and every think enable... I "disable" some options but im not sure wich one was the one to fix it.
Im not sure now, but that options when i changed from "enable" to "disable" the games work on disk channel.
Could be just one option, but i think its one of this...
[IOS Reloading] - Disable
[Disc Area Check] - Disable
[Force Disc Region] - Disable