Server Script
local event = Instance.new("RemoteEvent")
event.Parent = game.Workspace.Remotes
event.Name = "PartInvoke"
event.OnServerEvent:connect(function(player)
p.Parent = game.Workspace
game.Workspace.Lol.Transparency = 0.5
end)
LocalScript
local p = Instance.new("Part")
p.Name = "Lol"
game.Workspace.Remotes.PartInvoke:FireServer(p)
Error: Workspace.RemoteServer:6: attempt to index global 'p' (a nil value)

2 comments
You should be able to debug this yourself. The error tells you p doesn't exist for some reason. Look at lines 5 and 6.
I still don't get it on how to debug it by myself....