local MT = {}
function MT:__gc()
  self.cnt = self.cnt + 1
  if self.cnt == 1 then
    print("finalizing...")
  else
    print("and again...")
  end

  setmetatable(self, MT) -- here the error occurs
end

do
  local Collectable = {cnt = 0}
  setmetatable(Collectable, MT)
end

collectgarbage()
collectgarbage()
collectgarbage()
collectgarbage()