my script runs properly when going through it the first time but the second time i get an error?

16:11:26.077 - The Parent property of Model1 is locked, current parent: NULL, new parent Workspace

model1 = game.ReplicatedStorage.Model1:Clone()
model2 = game.ReplicatedStorage.Model2:Clone()

repeat
	model1.Parent = workspace
	model1:MakeJoints()
	wait ("10")
	if model1 then
		model1:destroy()
	end
	wait ("10")
	model2.Parent = workspace
    model2:MakeJoints()
	wait ("10")
	if model2 then
		model2:destroy()
	end
	wait ("10")

until false

I have a a feeling MakeJoints() locks the parent. Something you are doing is locking it.