Manually putting in the ban request into console will work for you:

ma_ban <player name, partial player name, steam id or user id> <ban time>

If you don't put in a number (greater than 0) in the variable for ban time it WILL permanently ban them. Big no-no unless you caught them hacking, etc. It will ban by the information you put into the console; i.e. it will be a "ban-by-name" if you put the players name in, "ban-by-steamID" if you put the players steam ID in, etc.