vrdude: usbdev_open(): did not find any USB device "usb" ARDUINO UNO R3 + MAC OS

Hello everybody, I've a brand new Arduino Uno R3 board that always give this error: vrdude: usbdev_open(): did not find any USB device "usb"

What happened.... I've open the box connected to my mac OS X 10.8 I've uploaded one sketch (rgb fade sketch) and it worked. I've reuploaded the sketch 2 o 3 times just for change the delay time and it worked. I'd like tu reupload the sketch with the final value for delay but now it always give me the error vrdude: usbdev_open(): did not find any USB device "usb"

I've checked this page http://arduino.cc/en/Guide/Troubleshooting#upload but nothing change, still vrdude: usbdev_open(): did not find any USB device "usb" I've also tried another mac os x 10.8 and also a win7 64bit. Still the same error.

When I reset the board the L led blinks for 2-3 sec and then the light remain on. The ON green led is lighted. But when I try to upload firmware the tx and rx leds don't blink. Any suggestion for my board?

In preferences, turn on verbose output.

Then copy and paste the results of the log part of the window here (putting the log between tags[[b][/b]/code]).

Thank you very much for your answer

Binary sketch size: 1,446 bytes (of a 32,256 byte maximum)
/Users/djlol/Desktop/Arduino.app/Contents/Resources/Java/hardware/tools/avr/bin/avrdude -C/Users/djlol/Desktop/Arduino.app/Contents/Resources/Java/hardware/tools/avr/etc/avrdude.conf -v -v -v -v -patmega328p -carduino -P/dev/tty.usbmodemfa131 -b115200 -D -Uflash:w:/var/folders/ck/lqv_tbw53zx78dlh_jyck2mh0000gn/T/build6126363073999491294.tmp/led_fading.cpp.hex:i 

avrdude: Version 5.11, compiled on Sep  2 2011 at 18:52:52
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2009 Joerg Wunsch

         System wide configuration file is "/Users/djlol/Desktop/Arduino.app/Contents/Resources/Java/hardware/tools/avr/etc/avrdude.conf"
         User configuration file is "/Users/djlol/.avrduderc"
         User configuration file does not exist or is not a regular file, skipping

         Using Port                    : /dev/tty.usbmodemfa131
         Using Programmer              : arduino
         Overriding Baud Rate          : 115200
avrdude: Send: 0 [30]   [20] 
avrdude: Send: 0 [30]   [20] 
avrdude: Send: 0 [30]   [20] 
avrdude: ser_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding

avrdude done.  Thank you.

Saturday I've bought a new board and everything works correctly. So my old (1 day of life) board is dead? How does the warranty work? I'm italian, so I could contact directly Arduino Italy?

From: http://arduino.cc/en/Main/ContactUs

Support If you own an official Arduino board and you believe it is defective, please email support (at) arduino.cc specifying the model, serial number, version of the operating system you use and version of the Arduino software.