SetTitle a nil value?

I have a dermamenu and when i use the console command to run the function is makes a error

 lua/autorun/client/cl_core.lua:6: attempt to call method 'SetTitle' (a nil value)

My line 6 is this

local DermaFrame = vgui.Create( "DFrame" )
DermaFrame:SetTitle( "Shop" )

Please tell me whats wrong with this ?

Show me the whole menu code