Remote Events not working properly?

I decided to try remote events with my spawning script. However, they are not working as I'm new to remote events. The event does fire, the server script isn't picking it up though.

Server Script (in ReplicatedStorage):

train = game.ReplicatedStorage.C70Freight
Camera = workspace.CurrentCamera
DriveFrame = GUI.Screen.DriveFrame
Spawning = GUI.Screen.Spawning
		
script.Parent.Parent.Events.C70Spawn.OnServerEvent:connect(function(player)
		GUI = player.PlayerGui.MainMenuGui
		DriveFrame.Visible = false
		Spawning.Visible = true
		Spawning.Text = "Spawning..."
		wait(0.01)
		local clone = train:Clone()
		clone.Parent = workspace
		clone:MakeJoints()
		wait(1)
		player.Character.HumanoidRootPart.CFrame = CFrame.new(610.265, 6.551, -3143.202)
		Spawning.Visible = false
		player.CameraMode = "Classic"
		Camera.CameraType = "Custom"
		Camera.FieldOfView = 80
		wait(1)
		GUI.Screen.IntroMusic:Stop()
end)

LocalScript (in Gui)

Frame = script.Parent.Parent
C70 = Frame:WaitForChild("Set1")
Player = game.Players.LocalPlayer

function C70Clicked()
	if workspace:IsRegion3Empty(Region3.new(Vector3.new(467.505, 6.548, -3076.283), Vector3.new(1152.544, 6.559, -3298.865))) then
	game.ReplicatedStorage.Events.C70Spawn:FireServer()
	else
script.Parent.Text = "Spawn Occupied! Please Wait."
wait(1)
script.Parent.Text = "4 Wagons"
	end
end

C70.MouseButton1Click:connect(C70Clicked)

Your problem is that you are trying to access the player from the server. This works fine in studio, but in the real game, the player's class is empty. The line

GUI = player.PlayerGui.MainMenuGui

would be the error point as the MainMenuGui would not exist from the server's point of view.

Hopefully this can clear some things up for you (the Remote Event works fine).