[MaxDeMan1]

I have looked at other posts on this topic but most are old/don't help. I'm trying to get this working on Left 4 Dead 2 specifically but i think its about the same for most source games.

[Bacardi]

...singleplayer is when you run server or your own game with maxplayers 1


But, if you want run mods in your own game, not using dedicated server, start your game -insecure mode.
*edit
However, MetaMod:source and SourceMod not support this method. It is recommended to use Source Dedicated Server (SRCDS)