Need help with key sais error

[swapinamnesia]

Hi im trying to make my first amnesia map i did a map with a key and a door that was locked but when i try to load the map in amnesia this error pops up

FATAL ERROR

FATAL ERROR: Could not load script file custom_stories/TheHauntedCellar/maps/TheHauntedCellar.hps! main (13,16) : ERR : Key_1 is not declared

What does that mean??? and heres my script in the hps file

void OnStart()
{

AddUseItemCallback("", "Key_1", "door_1", "UsedKeyOnDoor", true);

}

void FUNCTION(string &in item, string &in door)
{

SetSwingDoorLocked("door_1", false, true);
PlaySoundAtEntity("", "unlock_door", "door_1", 0, false);
RemoveItem(Key_1);

}

Could anyone help me have been searching on youtube and google for a solution but i cant find any please help.