Tabs on Property Sheet

So I have made a property sheet with two different tabs, but for some reason, the tabs themselves are not appearing, it looks like this:

[lua] local PropertySheet = vgui.Create( “DPropertySheet”, Menu )
PropertySheet:SetPos( 5, 45 )
PropertySheet:SetSize( 390, 600 )

PropertySheet:AddSheet("Leaderboards", LeaderBoards(), "icon16/application_view_columns.png", false, false)
PropertySheet:AddSheet("Unlocks", Unlocks(), "icon16/lock.png", false, false)

[/lua]

Here is the PropertySheet code^

Does anyone know what I’m missing?