title: Error while making a SENT using Derma GUI in Gmod
body: <p>I am making a SENT in Gmod with Lua and I want it to have a simple GUI menu using Derma. I have put the following into my cl_init.lua file:</p>
  
  <pre><code>local plantwinow = vgui.Create("DFrame")
  plantwinow:SetSize(202, 102)
  plantwinow:Center()
  plantwinow:SetTitle("Level " +lvltext +" Plant")
  plantwinow:SetDraggable(true)
  plantwinow:SetSizable(false)
  plantwinow:ShowCloseButton(true)
  plantwinow:MakePopup()
  </code></pre>
  
  <p>This gives me the error </p>
  
  <pre><code>prog.lua:1: attempt to index global 'vgui' (a nil value)
  </code></pre>
  
  <p>How can I fix this?</p>