Problem with making VGUIs

[OMGOMG132]

So im trying to make VGUI with buttons and everything for my weapon. This is the code:

function SWEP:Reload()
local form = vgui.Create("DFrame")
form:SetTitle("Test")
form:SetPos(5,5)
form:SetSize(10,10)
form:MakePopup()
end

this is the error:

[ERROR] addons/omg_weapons/lua/weapons/main_admin/shared.lua:115: attempt to index global 'vgui' (a nil value)
1. unknown - addons/omg_weapons/lua/weapons/main_admin/shared.lua:115

thanks to who ever will help :)

[Ghost_Sailor]

You're trying to call it serverside.
Put this on it.

if CLIENT then
--code
end

[OMGOMG132]

ok thanks