error - trying to index local (nil value) ??

so when, I try to get a player by using the GetPlayerFromCharacter() method I get an error saying "trying to index local (nil value)" or something like that, I cant remember what exactly it said, then I try to using a local script to get a local player but the same goes, I know my codes area 100% right. But the question is why do I keep getting an error when trying to get a player ?

please help.

thank you