I cheated in a greiseus orb when I did a WiFi program (got a level 100 arceus too!) and I gave it to my giratina and nothing happened, so I got annoyed and gave it to my friend who plays platinum version and it work just fine, what did I do?
You probably weren't playing Platinum version, because only in Platinum, HeartGold, SoulSilver, and beyond was Giratina able to switch forms. Diamond and Pearl could not.
