? Need help with this Regen Script.

--Hello, I'm a new scripter just getting into the fun of it and I've made this script that checks for int values and upon certain values changes the color of a brick and eventually breaks apart the blocks(it's supposed to do that) and everything in this script works just like I want it to.. except for my regen function (the first function) when I click my regen button on my GUI for the first time it works... however when I try to regen it a second time I get an error saying that

("The Parent property of SDoor is locked")

I'm not sure what this means and upon searching google I came up with nothing ? A little bit of help to enlighten me on what I'm doing wrong would be very much appreciated! I've included a screen shot of the error below

IMAGE LINK: http://imageshack.com/a/img834/284/ruvl.png

copy=game.Workspace.SDoor.SDoor:Clone()

function regen()
modd=game.Workspace.SDoor
modd2=game.Workspace.SDoor.SDoor
wait(.2)
zt=modd2:clone()

wait(.2)

modd2:Destroy()

wait(.5)

copy.Parent=nil
copy.Parent=modd

wait(.2)

modd.safelight.hold.Value=0

wait(.2)

check()

end

function check()

while true do

wait(.5)

 door=script.Parent.Parent.SDoor:GetChildren()

modd2=game.Workspace.SDoor.SDoor

h=script.Parent.hold.Value
modd=game.Workspace.SDoor.SDoor:GetChildren()

screen=script.Parent.light

value=modd2.Value

rk=modd2:clone()

if value.Value==1 then

regen() break

end

if h <5 then

screen.BrickColor=BrickColor.new("Lime green")  

for j = 1,#modd do

if modd[j].Name=="Part" then

modd[j].CanCollide=true

end
end 

end

if h >=700 then 

screen.BrickColor=BrickColor.new("Bright yellow")

end

if  h >= 1200 then

for i = 1,#modd do

if modd[i].Name=="Part" then

modd[i].Anchored=false  
screen.BrickColor=BrickColor.new("Really red")

end
end 
end
end
end

check()