its a problem with the pbsetup.run program or you may not be executing the way it needs to be run (I dont have knowledge on PunkBuster, I am talking purely from shell script perspective). try this:
cd <path to pbsetup.run folder>
sudo sh ./pbsetup.rn
If this still doens not help, you may have check line 18 of pbsetup.run file.
Don't fix it if it ain't broken, don't break it if you can't fix it -Husse