go to your pops.txt and make sure that cwcheatpops.prx is there. make sure it's not in two different txt's either, so check all the .txt's in your plugins folder just for sng's. wait until the game is completely loaded before attempting to start it up. like geek9 said, unless you are planning to hack all your own codes from the start, you'll need to check your game ID.
File Details-CWCheat-Database-Editor-v2.0-PSP-Homebrew-Applications -
use that to look in the pops database and see if they have an id in there for you to use. that might make things slightly easier for you.