Try Bebop https://forums.alliedmods.net/showthread.php?t=110210
if that don't work try Multislots https://forums.alliedmods.net/showthread.php?t=132408
I've did use Multislots for over 2 years with no issues, that is up until the 2nd July Steam update which gave me error after error filling up entire log files. I now use Bebop which has no issues at all.
You need to add these to your server.cfg:
sv_removehumanlimit "1" is no longere needed since the update
assuming you using the updated L4DToolz https://forums.alliedmods.net/showth...ight=sdk+tools