Did you wrote the Remote Control (RCon) password before writing a command in the console (only if you are using in your server)?
You must write the RCon password first to have access to the server rights to control the server. Make sure you wrote the correct password of RCon otherwise the RCon will tell you that the password is incorrect! When you wrote the password always type "rcon mp_antispeeder 2" (without quotes) like this:
1
rcon mp_antispeeder 2
If the problem still persist then you must give a proper information in your thread to see what's the problem.
If you have dedicated server, you need to enter rcon password first but you need to be in RCon Users List before.
Step 1 - be sure that you're in RCon Users List: sv_rconusers
Step 2 - enter RCon's password into console: rcon_pw
Step 3 - use all commands you want prefixed by rcon rcon
Maybe you could try explaining HOW it doesn't work. Did you see a speedhacker and the mp_antispeeder didn't kick him? Or did you set up some speed for another player and then he wasn't kicked for speeding? Or what? Explain the situation properly instead of going "why","are you serious","are you kidding me" and so on. It's not a proper way to behave anyways. We're trying to help you and you're being aggressive over it.
Did you tried to type the RCon password and write the command (as i said in my first reply) instead of changing the setting in the menu server to see if is work?