Also, you need to make sure the PnkBstrA.exe and PnkBstrB.exe are running in the background. They are serviecs that are required for punkbuster to run properly ingame. Some people (like myself), turn these off when I dont need them and from time to time, i forget to start the service before I go into game. I get kicked than I'm like "oh, duh!"
That should be done automatically when you load the game. I've never had to start the punkbuster services manually.