I don't get what's wrong with the script?

Why won't the door move?

Output 15:22:03.117 - Workspace.Model.Script:34: bad argument #2 to '?' (Vector3 expected, got userdata) 15:22:03.118 - Script 'Workspace.Model.Script', Line 34 15:22:03.120 - Stack End

local O = script.Parent.Open
local C = script.Parent.Close
local D = script.Parent.Union

opened = false 

function Door() 

if not opened then 

		opened = true 
        script.Parent.Cog1.Script.Disabled = false
        script.Parent.Cog2.Script.Disabled = false
		O.Sound:Play()     
        O.Transparency = 1
		C.Transparency = 0
		wait(5)
	    for i = 1, 4600, -0.01 do		
		D.CFrame = Vector3.new(D.CFrame + CFrame.new(0,i,0))
		wait(.01)
		end 
	end 


if opened then 

		script.Parent.Cog1.Script.Disabled = true
        script.Parent.Cog2.Script.Disabled = true
		C.Sound:Play()       
        O.Transparency = 0
		C.Transparency = 1
		wait(5)
	    for i = 1, 4600, 0.01 do		
		D.CFrame = Vector3.new(D.CFrame + CFrame.new(0,i,0))
		wait(.01)
		end 
	end 

		opened = false 

	end
 
script.Parent.Close.ClickDetector.MouseClick:connect(Door)
 
script.Parent.Open.ClickDetector.MouseClick:connect(Door)