(GUINAME) Is not a valid member of PlayerGui error?

Whenever I try to access a child of PlayerGui ingame (in studio it works fine), it says that GUINAME is not a valid member of PlayerGui. If I use :WaitForChild, it says 'infinite yield possible'.

This is a SCRIPT located in a part in workspace. All the GUIs are valid members of PlayerGui; the script just doesn't think they are.

SCRIPT:

local part = script.Parent

--VALUES--
local shopDebounce = game:WaitForChild("ReplicatedStorage"):waitForChild("Values"):waitForChild("shopDebounce")
_G.shopBlockHitVal = false

--CAMERA--
local Camera = workspace.CurrentCamera
cameraPart = workspace.cameraPart

part.Touched:connect(function(hit)
	if 	_G.shopBlockHitVal == false then
		print("no")
		wait(1)
		_G.shopBlockHitVal = true 
		print("works")
		local h = hit.parent:FindFirstChild("Humanoid")
		if h and shopDebounce.Value == false then
			print("workin'")
			shopDebounce.Value = true
			local tweenPosition = coroutine.wrap(function()
				local player = game.Players:GetPlayerFromCharacter(hit.Parent)
				player.PlayerGui.shopScreenGui:WaitForChild("mainFrame"):TweenPosition(UDim2.new(0.5, 0, 0.5, 0), "Out", "Quad", 1) --Error
			end)
			local blurEffect = coroutine.wrap(function() --blur
				print("k")
				for i = 0, 20, .25 do
					game.Lighting.Blur.Size = i
					wait(.1)
				end
			end)
			local cameraChange = coroutine.wrap(function()
				repeat wait()
					Camera.CFrame = cameraPart.CFrame
					Camera.CameraType = Enum.CameraType.Scriptable
				until Camera.CameraType ==  Enum.CameraType.Scriptable and Camera.CFrame == cameraPart.CFrame
			end)
			local fadeIn = coroutine.wrap(function()
				for i = 1, 0, -0.05 do 
					local player = game.Players:GetPlayerFromCharacter(hit.Parent)
					local fadeFrame = game.Players:GetPlayerFromCharacter(hit.Parent):WaitForChild("PlayerGui"):WaitForChild("fadeEffect"):WaitForChild("Frame") -- Error
					fadeFrame.BackgroundTransparency = i
					wait(.02)
				end	
			end)
			local fadeOut = coroutine.wrap(function()
				for i = 0, 1, 0.05 do 
					local player = game.Players:GetPlayerFromCharacter(hit.Parent)
					local fadeFrame = game.Players:GetPlayerFromCharacter(hit.Parent):WaitForChild("PlayerGui"):WaitForChild("fadeEffect"):WaitForChild("Frame")  -- Error
					fadeFrame.BackgroundTransparency = i
					wait(.02)
				end				
			end)
			fadeIn()
			blurEffect()
			wait(.75)				
			cameraChange()
			wait(2)
			fadeOut()
			wait(.1)
			tweenPosition()
		end
		wait(1)
		shopDebounce.Value = false
	end
end)

Thanks!