To Run The Following Commands To Play Left For Dead
Makes the game not crash		

mat_queue_mode 0

To plan lan play

For the host, in console
1. Type: ip xxx.xxx.xxx.xxx	 (for example ip 5.200.200.1)
2. Type: sv_allow_lobby_connect_only 0
3. Type: net_start
4. Type: map (select the map you wanna play from the list)

For the players, in console, 
Type: connect xxx.xxx.xxx.xxx (example: connect 5.200.200.1)

To play usung Hamachi replace you IP address with your Hamachi IP

Set difficulty: z_difficulty (Easy, Normal, Hard, Impossible)