How to search a player's backpack?

This is the code:

script.Parent.Slot.MouseButton1Down:connect(function()
	playerName = script.Parent.Slot.Text
	print(playerName)
	local backpack = game.Players:FindFirstChild(playerName).Backpack
	print(backpack)
	local toolFrame = script.Parent.Parent.ToolFrame.Tool	
	for i,tool in pairs(backpack:GetChildren()) do
	print("ok")
	if tool then
	local tool = toolFrame:Clone()
	tool.Parent = script.Parent.Parent.ToolFrame
	tool.Name = "Tool"--..slotnum
	tool.Position = UDim2.new(0,0,0,55*num.Value)
	tool.Text = tool.Name
	tool.Visible = true
	end
	end
end)

The function works until the for loop. But I'm not getting any error. What am I doing wrong? Help is greatly appreciated!

Maybe the "toolFrame" cannot be found OR the backpack array is empty, make sure you debug the code.