Player:IsInGroup error: Player not in datamodel error?

I have a script which will show an Image above the heads of players in a certain group and whenever somebody leaves the game, this error will appear:

Player:IsInGroup error: Player not in datamodel Stack Begin Script 'ServerScriptService.Overhead GUI', Line 5 - global onPlayerRespawned Script 'ServerScriptService.Overhead GUI', Line 26 Stack End

Here is the script in ServerScriptService:

local groupID = GROUPIDHERE

function onPlayerRespawned(newPlayer)
	wait(1)
	if newPlayer:IsInGroup(groupID) then
		local gui=Instance.new("BillboardGui")
		gui.Parent=newPlayer.Character.Head
		gui.Adornee=newPlayer.Character.Head
		gui.Size=UDim2.new(3,0,3,0)
		gui.StudsOffset=Vector3.new(0.5,2,0)
		local text=Instance.new("ImageLabel")
		text.Image = "rbxgameasset://Images/Photo"
		text.Size=UDim2.new(1,0,1,0)
		text.Position=UDim2.new(-0.225,0,-0.35,-45)
		text.BackgroundTransparency = 1
		text.Parent=gui
		print(newPlayer.Name.. " is a member of group")
	end
end

game.Players.PlayerAdded:Connect(onPlayerRespawned)

function onPlayerEntered(newPlayer)
	newPlayer.Changed:Connect(function (property)
		if (property == "Character") then
			onPlayerRespawned(newPlayer)
			print("Reloading " ..newPlayer.Name.. "'s GUI")
		end
	end)
end

game.Players.PlayerAdded:Connect(onPlayerEntered)

How can I solve this error? Thanks