I bought a new Arduino Ethernet Shield and connect it to Arduino Uno. When I uploaded my code, I got the error avrdude: stk500_recv():programmer is not responding. Without the Ethernet Shield, it could run succeed. I have tried all the solutions on the Internet. Mac os 10.10.5 and Arduino 1.6.10. The board I chose is Arduino Uno and serial port is dev/cu.usbmodem1421. I have tried to reset and reinstall Arduino IDE，and downloaded FTDI driver. These solutions are not working.
Any help will be appreciated!
Thanks!