Recently, BattlEye has been blocking players from joining Insurgency servers. Until this issue is resolved, the temporary fix is to disable BattlEye altogether on your server. Keep in mind that disabling anti-cheat will allow certain cheats to become possible.

If your server is running the "custom" playlist, all you need to do is set this cvar in your server's root config file (probably server.cfg):

After restarting your server, players should be able to join again.

If you are using one of the NWI playlists (not "custom"), it will force sv_battleye to be enabled. If you try to disable it manually, it will automatically re-enable.

Download this plugin[forums.alliedmods.net]. (Click "Get Plugin".)

Copy the file to your server, and place it here:

Restart your server.

You may wish to allow server admins to change this setting on-the-fly. For this, you can compile and install Bot Chris' plugin from this comment.

Open the SourceMod compiler page[www.sourcemod.net].

Enter the "plugin short name" as no_battleye

Copy the code in from Bot Chris' comment linked above.

Click "Compile", and you should see "Your plugin successfully compiled!" at the top of the page. Click the download link below it. This will download the compiled plugin, a file called "no_battleye.smx".

Place this file here on your server:

Restart your server.