Arduino UNO + Yun Shield

Good evening to all, I am new in the forum and I write for a kind help with arduino R3+yun shield. I have connected the shield over arduino and placed the jumper to as explained here: The Arduino is powered with a 9V power supply. Nothing esle is connected to the board.

I have configured the yun shield with the webserver and i correctly reach it over my wifi lan.

The problem is that i am not able to upload anything on arduino (tried with blink exemple): i try to upload the .hex file... Then i have tried to plug the arduino itself (no jumper and no yun shield) via usb to my mac but i cannot program the board: the led 13 is always on, the board does not reset and the ide show the error "avrdude: stk500_getsync()" error.

Before trying the yun shield the arduino was working correctly. It's the second arduino with the same problem :((

Thanks in advance for your help. Andrea