It looks like your using Arduino 1.0. The PID_Beta6 library wasn't written for the new release. I believe the author has updated the library for Arduino 1.0, see here: http://arduino.cc/pl...Code/PIDLibrary
But the guaranteed process is to use the older Arduino 0021 since haven't yet rewritten the KSlibs and Sketch code for 1.0 and you'll likely get compile errors from those.
Hope that helps.