Arithmetic Error? [Solved]

Im trying to make this plane Bank in the direction of the mouse. But I get this error on line 9

"15:13:06.446 - Players.Player1.Backpack.Plane.Main:10: attempt to perform arithmetic on global 'maxBank' (a nil value)"

wait(0.1)	-- Yes, this is needed. If it's not here, the plane will only work once.
local player = script.Parent.Parent.Parent
local mouseSave
local maxbank = 90
local gyro = script.Parent.Parent.Parent.Character.Real.Main.Gyro

function fly(m)	-- Main function that controls all of the flying stuff. Very messy.
	while true do
		local bank = ((((m.ViewSizeX/2)-m.X)/(m.ViewSizeX/2))*maxBank)	-- My special equation to calculate the banking of the plane. It's pretty simple actually
		bank = (bank < -maxBank and -maxBank or bank > maxBank and maxBank or bank)
			gyro.maxTorque = Vector3.new(math.huge,math.huge,math.huge)
			gyro.cframe = (m.Hit*CFrame.Angles(0,0,math.rad(bank)))
			wait()
		end
		wait()
	end

script.Parent.Selected:connect(function(m)	-- Initial setup
	mouseSave = m
	game.Workspace.CurrentCamera.CameraType = Enum.CameraType.Attach
	m.Icon = "http://www.roblox.com/asset/?id=48801855"	-- Mouse icon used in Perilous Skies
	delay(0,function() fly(m) end)	-- Basically a coroutine
	end)

You made a syntax error. You were trying to perform arithmetic on maxBank, when the variable name is actually maxbank. The "b" in the variable name is actually lowercase.