Being kicked for having an "empty cdkey" ?
If you are being kicked for an empty cdkey error it means that your game has tried to unsuccessfully to comunicate with PunkBuster, as this where your game cdkey is generated.
You need a cdkey to be able to play on any PunkBuster enabled game server.
Once you have recieved this error there are two things you can try while you are still in game to rectify this error and start playing right away.
1. In console type /pb_cdkeyreg this makes PB try to register a cd key.
2. In console type /pb_cdkeyver this verifies that your cd key is getting sent from PunkBuster.
You should almost straight away get a cdkey from PuinkBuster.
It should take no longer a couple of minutes.
To test if you receieved your cdkey type into the console /pb_myguid as an answer to this right away in the console you should be able to see your cdkey and your GUID. If you can you can now join any PunkBuster enabled server.
If you still have not got a cdkey you need to quit ET and go back to desk top.
Having tried the above and it has not worked you need to test if your computer can actually find PunkBuster.
To test this do the following.
Enter the following commands in the windows commandline (dos-box), by pressing Start-button, select "Run" and type "cmd"
and then after the command promt type :
ping -n 20 etguidauth.evenbalance.com
If the two commands you entered where successful then you need to try step 1 again.
When the ping shows 100% loss and you have access to the internet, try the following
Find the hosts file in C:\WINNT\system32\drivers\etc\ and open it with a plain text editor.
Add 188.8.131.52 etguidauth.evenbalance.com as the last line, then save the file and try playing again.
If you encounter any problems in future, remember to remove that line from the hosts file again.
You can also try disabling software like Process Guard has helped users too if you have it.