Loading Assets Gui not working in server mode?

Errors

First of all,lets look at the code you have

local contentprovider = game.ContentProvider
local frame = script.Parent.Frame

while wait() do
   if contentprovider.RequestQueueSize == 0 then
frame:TweenPosition(Udim2.new(0,0,-1,0),"In","Quart",1)
wait(1)
script.Parent:Destroy()
end
end

Error #1 Content Provider is a service,you can't call it by game.ContentProvider You will have to use game:GetService("ContentProvider")

I will provide something for your player added script. I recommend putting the gui as a child of the player added script since replicated storage is also a service

local gui = script.NameOfGUI
game.Players.PlayerAdded:Connect(function(plr)
	local plrgui = plr.PlayerGui
	local clone = gui:Clone()
	clone.Parent = plrgui
end)

Lets go back to your main script Error #2 What are you trying to load?If you want to use RequestQueueSize, you need something to load,try publishing what you are trying to load,something like this:

--Example script
local ContentProvider = Game:GetService("ContentProvider")
 
-- load a bunch of assets
local assets = {2253543, 2434541, 5133543, 2423433}
for _, asset in ipairs(assets) do
	ContentProvider:Preload("http://www.roblox.com/asset/?id=" .. asset)
end
 
-- wait for them to complete
while ContentProvider.RequestQueueSize > 0 do
	wait(0.1)
end

Error#3 What is script.parent.Frame?Your script should be in the frame itself,not the screengui.Also,you should :Destroy() the whole screengui

Lets fix the errors and put in in a script

local asset = idofmodel
local frame = script.Parent

game:GetService("ContentProvider"):PreloadAsync({ "http://www.roblox.com/asset/?id=" .. asset })


while game:GetService("ContentProvider").RequestQueueSize > 0 do
	wait(0.1)
script.Parent.Load.Text = "Assets Remaining:".. game:GetService("ContentProvider").RequestQueueSize 	
end

if game:GetService("ContentProvider").RequestQueueSize == 0 then
	
	frame:TweenPosition(UDim2.new(0,0,-1,0),"In","Quart",1)
	wait(1)
	frame.Parent:Destroy()
end

make sure it is a local script any errors please comment below