How do I fix this error?

I have a big mess of code of a pot that shatters into pieces when damaged enough and I get this error:

16:00:53.380 - The Parent property of Shatter is locked, current parent: NULL, new parent NPC 16:00:53.381 - Script 'Workspace.NPC.PotScript', Line 86

I made as a model so it will be easier to understand: http://www.roblox.com/plz-halp-meh-plez-item?id=280487754

I have seen some people ask the same question but the answers don't help in my case.

Here is the code:

local i = 1

script.Parent.Pot.Anchored = true
script.Parent.Humanoid.MaxHealth = math.huge

script.Parent.Head.Transparency = 1
script.Parent.Torso.Transparency = 1

for c = 1, 37 do
    local sha=script.Parent.Shatter["a"..c]
    sha.CanCollide=true
    sha.Transparency=1
end

backup=script.Parent.Shatter

model = backup:clone()

px = script.Parent.Pot.CFrame.X
py = script.Parent.Pot.CFrame.Y
pz = script.Parent.Pot.CFrame.Z
ny = pz + 10000





function killpot()

        for a = 1, 37 do
            script.Parent.Head.CFrame   =   CFrame.new(px, ny, pz)  * CFrame.Angles(0, math.pi, 0)
            script.Parent.Torso.CFrame  =   CFrame.new(px, ny, pz)  * CFrame.Angles(0, math.pi, 0)          
            script.Parent.Pot.CFrame    =   CFrame.new(px, ny, pz)  * CFrame.Angles(0, math.pi, 0)          
            local shat=script.Parent.Shatter["a"..a]    
            shat.Transparency=0
            shat.Anchored=false
        end
        wait(1.5)

        for g = 1, 37 do
            local shatte=script.Parent.Shatter["a"..g]      
            shatte.Anchored=true
        end

        for b = 1, 37 do
            local shatt=script.Parent.Shatter["a"..b]           
            wait(0.01)      
            shatt.Transparency=0.1
            wait(0.01)
            shatt.Transparency=0.2
            wait(0.01)
            shatt.Transparency=0.3
            wait(0.01)
            shatt.Transparency=0.4
            wait(0.01)
            shatt.Transparency=0.5
            wait(0.01)
            shatt.Transparency=0.6
            wait(0.01)
            shatt.Transparency=0.7
            wait(0.01)
            shatt.Transparency=0.8
            wait(0.01)
            shatt.Transparency=0.9
            wait(0.01)
            shatt.Transparency=1
            wait(0.01)      
        end
    end


local i=1

while i < 10 do
    local i = 1
    wait(0.1)
    if script.Parent.Humanoid.Health < 50 then
        script.Parent.Humanoid.Health = math.huge
        script.Parent.Shatter.a37.Sound:Play()      
        killpot()
        script.Parent.Shatter:Destroy()
        print"wait 10"      
        wait(1)
        model.Name = "Shatter"
        model.Parent = script.Parent     --This is line the error appears
        script.Parent.Pot.CanCollide = true
        script.Parent.Pot.Transparency = 0
        script.Parent.Humanoid.Health = 100     
        script.Parent.Head.CFrame   =   CFrame.new(px, py, pz)  * CFrame.Angles(0, math.pi, 0)
        script.Parent.Torso.CFrame  =   CFrame.new(px, py, pz)  * CFrame.Angles(0, math.pi, 0)          
        script.Parent.Pot.CFrame    =   CFrame.new(px, py, pz)  * CFrame.Angles(0, math.pi, 0)
    end
end

Sorry for it being such a mess I am a beginner at scripting.