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
cd /System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns 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.