Most problems with a Left 4 Dead 2 server come down to a few causes. Start with the one that matches what you see.
Nobody can connect, or players are refused straight away when typing the address
Why: Lobby connections only is on. It refuses anyone who did not arrive through a Steam lobby, including direct connections. A new server starts with it off, so it is on only if someone turned it on.
Fix: If it was turned on, turn Lobby connections only off in the server's settings and restart the server.
Max Players is 8 but only 4 people can play together
Why: The game's campaigns are built for four survivors. A stock server never lets more than 4 humans and bots into a coop, survival or scavenge game, and a direct address connection stays at 4 even in Versus.
Fix: Plan for 4 players. Direct connections hold 4 players.
The game console will not open when pressing the tilde key
Why: The developer console is off by default in the game.
Fix: In the game, go to Options, then Keyboard/Mouse, turn on Allow Developer Console, then press the tilde (~) key.
A new server name or game mode does not show up
Why: These are written into the server's config when it starts, so a running server keeps the old values.
Fix: Restart the server (a new server name also appears on the next map change). The game mode you choose is also the one shown to players in the browser.
The panel will not save the server name or Join password
Why: Only letters, numbers, spaces and basic punctuation are allowed, up to 63 characters for the name and 32 for the password.
Fix: Remove special characters or shorten the text, then save again.
An RCON client cannot connect
Why: The RCON password is empty, which leaves RCON disabled, or it was changed without a restart.
Fix: Set an RCON password (letters, numbers, underscores and dashes, up to 30 characters) and restart the server.
Players cannot join after Valve releases a game update
Why: Client and server are on different builds.
Fix: Make sure Auto Update is on and restart the server so it updates on start.
SourceMod plugin settings were reset
Why: SourceMod is added by reinstalling the server, which can reset plugin configs and delete other server files.
Fix: Before asking support to reinstall, download a backup of the left4dead2 folder, or at least left4dead2/addons/sourcemod/configs and your plugin config files, then restore them afterwards.
Players are stuck on a password window or cannot get in with the Join password
Why: Left 4 Dead 2 has a known game bug where the Join password is ignored or its password window hangs.
Fix: Clear the Join password under Settings, then Game Settings, and restart the server. Do not rely on a Join password to keep strangers out.
Still stuck?
Open a ticket in the category that fits and include the last 50 to 100 lines of the console. See How to open a support ticket and How to fix a server that will not start.
