trying to download an arduino program in Yosemite and not working?
The FTDI driver Apple wrote is the culprit.
disable the Apple FTDI driver first
sudo mv AppleUSBFTDI.kext AppleUSBFTDI.disabled
Download the new driver here: http://www.ftdichip.com/Drivers/VCP.htm
When Ive tried, the last version was v2.2.18: http://www.ftdichip.com/Drivers/VCP/MacOSX/FTDIUSBSerialDriver_v2_2_18.dmg
Install the new driver and happy arduino.