Why does my script only work in play solo but when I play with roblox player?

Here's my script v v v It always work when I play solo but NEVER when I try playing with roblox player. :/ It's suppose to replace only the shirt of the player when he/she touches the block...

Platform = script.Parent

Platform.Touched:connect(function(hit)
	local h = hit.Parent
	if h.ClassName ~= "Model" then
		return nil
	elseif h.ClassName == "Model" then
		h.Shirt.ShirtTemplate = "http://www.roblox.com/asset/?id=65387140"
	end
end)

Your method of checking to see if a Player hit your 'Platform' is easily broken. As well, the character may or may not have a Shirt object when you try to access it, you'll have to add one in if they don't. Try this code instead:

Platform = script.Parent

Platform.Touched:connect(function(hit)
    local h = hit.Parent
	if not Game.Players:GetPlayerFromCharacter(h) then return end
	if not h.Shirt then Instance.new("Shirt", h).Name = "Shirt" end
    h.Shirt.ShirtTemplate = "http://www.roblox.com/asset/?id=65387140"
end)

You took it from Free Modules I guess. What does output shows you?