You should not create a new world in an entity script. The world is already created for you.
MgetWorld = {}
function MgetWorld:Start()
self.pref = LoadPrefab(self.world, "pref/test_obj.pfb")
if self.pref ~= nil then
self.pref:Move(0.0, 0.0, 0.0)
Print("MgetWorld : done")
end
end
function MgetWorld:Update()
end