When I migrated to IDE 1.6.5r5, I had errors during compile. Modifying the digitalWriteFast.h file as mentioned by heX1625616 worked. I also had problems with the location of the digitalWriteFast directory; I had used the windows installer for the installation of the IDE. I now only use the portable (non Administrator version). I have to put the digitalWriteFast into sketch\libraries directory. I was also having problems with the Wire library until I installed it into the sketch\libraries directory.