Error uploading to Arduino UNO in Mac OS X Lion 10.7.5

I’ve tried to plug my Arduino UNO board to my Macbook Pro (using OS X Lion 10.7.5) for the first time (I’ve used it in a Windows environment previously and it did work) and I get an error uploading.

First of all I’ve chosen Arduino UNO as board and dev/tty.usbmodemfa131 as Serial Port, when I try to upload the blink example and I get the following error (while compiling both TX and RX green leds blink):

avrdude: stk500_recv(): programmer is not responding
processing.app.debug.RunnerException: Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
at processing.app.debug.BasicUploader.uploadUsingPreferences(BasicUploader.java:126)
at processing.app.Sketch.upload(Sketch.java:1664)
at processing.app.Sketch.exportApplet(Sketch.java:1623)
at processing.app.Sketch.exportApplet(Sketch.java:1595)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2393)
at java.lang.Thread.run(Thread.java:680)

Please let me know if you have any idea about this problem and how to solve it. I don’t have a PC, only my Mac and I need to make it work!

Thanks :%

Duplicate post deleted.
I can't help, not a Mac user.