SheetItem Derma Help!

[confuseth]

I am trying to make a menu for my server, wich displays rules and information in a tab

local PropertySheet = vgui.Create( "DPropertySheet", panel )
PropertySheet:SetPos( 50, 50 )
PropertySheet:SetSize( 800, 360 )
 
local SheetItemOne = vgui.Create( "DCheckBoxLabel" )
SheetItemOne:SetText( "Use Props?" )
SheetItemOne:SizeToContents()
SheetItemOne.Paint = function (self, w, h)
  draw.RoundedBox( 0, 0, 0, w, h, Color( 100, 100, 255, 255 ) ) 
end
 
local SheetItemTwo = vgui.Create( "DCheckBoxLabel" )
SheetItemTwo:SetText( "" )
SheetItemTwo:SizeToContents()
SheetItemTwo.Paint = function (self, w, h)
  draw.RoundedBox( 0, 0, 0, w, h, Color( 100, 100, 255, 255 ) ) 
end
PropertySheet:AddSheet( "Rules", SheetItemOne, "", false, false, "Rules must be obeyed!" )
PropertySheet:AddSheet( "Information", SheetItemTwo, "", false, false, "Information for this Gamemode!" )

I dont know how to properly make it, if you guys need the full code please say so

Error:

[ERROR] lua/vgui/dimage.lua:120: attempt to index local 'Mat' (a nil value)
  1. FixVertexLitMaterial - lua/vgui/dimage.lua:120
   2. SetImage - lua/vgui/dimage.lua:101
    3. Setup - lua/vgui/dpropertysheet.lua:26
     4. AddSheet - lua/vgui/dpropertysheet.lua:167
      5. unknown - lua/fone.lua:168

[IMG]https://i.gyazo.com/635f47ed015ef6696aac1797a068436e.png[/IMG]