Fable 3 Message Board  

I think the save is encrypted per hardware key. Maybe from a CPU serial, HDD serial etc.

I was about to post what DAB said. When you activate your game it's registered to a specific hardware, and maybe software, profile. That's how the copy protection works. When you activate it on another machine, even if it's in the same room with the same specs, the activation profile will still be different. There's probably some kind of correlation between that and saves, though I dunno why.

Though if it works for someone else, I'm just talking out of my ear.