Some people have reported an issue with the VUSB Arduino Library not working with the latest release of the Arduino IDE. This appears to because of an error in the library that is ignored in the older Arduino IDE but will cause it not to compile in the latest 1.6 release. I can confirm that it definitely does compile in 1.0.5. This error has been fixed in the original VUSB library but this fix has not made it's way through to the Arduino port. It is not ideal but the quick and easy solution is to downgrade the IDE to upload the firmware.