Here are more or less some things to solve the problem:

And if you tried in Versus mode. Here what you must do to enable it:

引用自 Maur0：

Here are more or less some things to solve the problem:

Remember

1. You need Admin System for this to work.
   
   
2. Avoid that none of the mods (marked in red) are in conflict.
   
   
3. It will work online if you're hosting a local server.
   
   
4. Always have the sv_consistency 0 command on the console or in an autoexec file. To avoid kicking players who enter by using mods on local server.
   
   
5. Make sure you have access to the admin system commands in an "admins.txt" file located in this folder: "C:/Program Files (x86)/Steam/steamapps/common/Left 4 Dead 2/left4dead2/ems/admin system".
   
   
6. If you have the file "server.nut" or some other type of file "vscripts" located here: "C:/Program Files (x86)/Steam/steamapps/common/Left 4 Dead 2/left4dead2/scripts/vscripts". Try that the commands scripts and codes are well done within the file, otherwise an error and the Admin System mod will not work and neither does the Admin Menu.

Note: If for any reason none of these options worked for you. The safest thing you can do is uninstall all your mods and download only the admin system and the admin menu. And step by step you see what mods work and what doesn't. Otherwise, try checking your game cache.

And if you tried in Versus mode. Here what you must do to enable it:

Versus / Scavenge with mods

To be able to play the versus and scavenge mode with the admin system, admin menu and other mods. They do these steps:

1. Locate and open "addonconfig.cfg" in "Left 4 Dead 2/left4dead2/cfg".
   
2. Change all "RestrictAddons" values to 0
   
3. Save changes and enjoy hosting your local versus and scavenge server.

Thanks, the last one seems to have fixed it.

One question though, will this disable achievements?

引用自 ENGLISHNAME：

One question though, will this disable achievements?

Only if you activate the command "sv_cheats 1". But since this mod does not require this command, it is 100% obtainable.