Why does it say "attempt to call a table value"?

I don't get why this doesn't work...

human.HealthChanged:Connect(function(d)
	game:GetService("TweenService"):Create(script.Parent, TweenInfo(0.1), {Size = UDim2.new(d / human.MaxHealth, 0, 1, 0)}):Play()
end)

The code is as shown above, but in the output it just prints "attempt to call a table value" and I don't know what that means. Any suggestions?