Hmm, that's an interesting one.
Is your save data corrupted by any chance? Go into the Memory Card manager thingy before loading a disk. Look at all your save files, find your Timesplitters 2 file, and if it's a purple cube (thinks it's purple) then basically your save is corrupted. If the proper picture of the save (E.g. Timesplitters 2 game box) is there, then your save file is fine.
If your save is alright, then I'm not sure what could be wrong with it, sorry. Unless there are other saves that are corrupted instead. Although that shouldn't really matter. If there are other corrupted saves, try copying everything, barring the corrupted saves, to another memory card and then formatting the memory card with the corrupted saves on and then move your save files back to that memory card. That MIGHT work, but I'm not too sure.
Sorry I couldn't be any more help.
Any thoughts from any other Staff?
Jay