Drugs Mod lua errors on "consumption"

I’m in the process of helping a friend set up a DarkRP server (God help me). I got a drug dealer class set up with custom shipments etc, the shipments spawn the entities but when you try to use the entities you get the following LUA error:

[ERROR] lua/entities/durgz_mushroom/shared.lua:94: bad argument #2 to 'Exists' (string expected, got nil)
  1. Exists - [C]:-1
   2. fn - lua/entities/durgz_mushroom/shared.lua:94
    3. unknown - addons/ulix/lua/ulib/shared/hook.lua:183

Line 94 in shared.lua is

if( file.Exists("../materials/VGUI/durgzmod/awesomeface.vmt") && pl:GetNetworkedFloat("durgz_mushroom_high_start") && pl:GetNetworkedFloat("durgz_mushroom_high_end") > CurTime() )then

Now i’m assuming it’s something to do with the fact he wants me to get a 4 year old addon working, but I have seen servers with this working recently, any help would be appreciated.

That function takes two arguments