Crash on startup, tried to index a nil value

Hey, I recently got a new gaming rig, and now GMOD doesn’t want to work. The error happens on startup when it reaches initializing serverside, it’ll just crash with the error “Engine Error: Lua Panic: Tried to index a nil value”
Yes, I’ve bought the game, yes i’ve tried reinstalling, yes, I have Half Life 2 (And Portal, Portal 2, CSS, CS:GO, Ep2, Ep1, Lost coast) and yes, it also happens when trying to start Garry’s Mod 13 Beta. Any idea’s guys? My specs are:
8gb of RAM, quad core i5, AMD Radeon HD 7800. Any help would be appreciated.

Im still having the issue, some help would be A+… bump …