help with in difficult savegame issue

maybe its me but I've got a problem it get complicated but maybe someone out there can help.

Ihave yu gi oh gx spirit caller on my ds lite on a ds firecard, my partner also has the same game, agian on a ds fire card. I wanted to transfer his savegame onto my card, but it wont work.
at first i tried just copying the sav file, that didn't work, i then copied his entire card including all system files and folders (systemdat and xmenu.dat) and copied them onto my card overwriting everything on my card, this didn't work it still only come up with my savegame, how can this be when i wiped my card? it's almost like it's stored on the ds itself, but if i put his card into my ds i get his savegame, so now I have two card identical in the files on them but one gives his save game and the other mine....whats going on?
It's driving me insane!!!!