ENT:KeyValue saying that the keyvalues have a nil value

[HiddenMyst]

[lua]
AddCSLuaFile( "cl_init.lua" )
AddCSLuaFile( "shared.lua" )
include( 'shared.lua' )

function ENT:Initialize()
floorCurrent = 0
floorTo = 0
end

//function TravelDelay(floorCurrent, floorTo)
// return ((floorTo-floorCurrent)*self:getKeyValue(elevator, "movedistance"))/self:getKeyValue(elevator, "speed")
//end

//KeyValues
function ENT:KeyValue(key, value)
if key == "doorprefix" then
doorPrefix = value
end

if key == "elevatorname" then
elevator = ents.FindByName(value)[1]
end

if key == "movedelay" then
moveDelay = value
end
end

//Input
function ENT:AcceptInput( name, activator, caller, data )
print("current: "..floorCurrent)
print("to: "..floorTo)
print("using: "..elevator)
if (name == "goto") then
if (floorCurrent!=floorTo) then
floorCurrentDoor = ents.FindByName(DoorFloorCurrent(floorCurrent))[1]
floorCurrentDoor:Fire("SetAnimation", "close", 0)
elevator:Fire("SetPosition", floorTo, moveDelay)
end
end

if (name == "updatefloor") then
UpdateFloor(floorCurrent, floorTo)
end
end

function UpdateFloor(current, to)
self.floorCurrent = current
self.floorTo = to
end

function DoorFloorCurrent(floor)
doorName = doorPrefix..floor
return doorName
end

function ENT:OnRemove()
end[/lua]

[lua\entities\elevator_controller\init.lua:36] attempt to concatenate global 'elevator' (a nil value)

It's kinda got me stuck and I don't know what I've done wrong to cause it. Can anyone please shed some light on the situation?