Gmod Half life 2 Co op Issue

I was simply wondering about when I played Garrysmod with my Girlfriend and we were gonna play Half life 2 Co op just from start to end I realised that most textures are missing like the part where you Talk to the vortigaunt and the guy in the Cart
and escape from there and you manage to kinda escape that Area there Is sand and straight forward line when you turn there Is Pure white Area like you can’t do anything like the rest of the map Is missing or big important parts

In Garry’s Mod for more than 3 years does not work changelevel for Half-Life 2 and episodes. This is not an error, you just did not load the next card.
Developers seem to have long ago spit on this, and Garry has been working on developing a new sandbox on UE4.

For co-op, use Synergy (for free on Steam). http://store.steampowered.com/app/17520/Synergy/

You will want to download a HL2 COOP gamemode for GMod to play half life 2 levels properly in multiplayer.