I had the same problem with my Arduino Uno last night. After I hit my head against the wall, I updated the Arduino IDE to 1.6.0. I did this on Mac OS X by simply downloading 1.6.0 from the Arduino homepage.
After installing this and choosing the right board in my case, something like: / dev / tty / usbmodem ____ (Arduino Uno)
The error was cured, and I could load the programs again without performing any complicated presses of reset, that is, one second after loading the program holds the reset button for 5 seconds.
Ok, this is what worked for me, hope it works for others!
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