Brick will not CFrame?

I have a light beam I want over a part. Well the part will be teleporting around the map at times so I need it to always move with the part. Right now the beam wont move to the part at all with no output errors. Any help?

local beam= script.Parent
local map = game.Workspace:WaitForChild("Map")
local cube = map:WaitForChild("Cube")
local cpos = cube.Position
local bpos = beam.Position

bpos.CFrame = CFrame.new(cpos)

Very small code I just don't understand why this is not working from what I see it should be fine.