Hi everybody.
Quick solution that worked for me: cut (or bend out) the reset pin from the ethernet shield. No solder, no capacitor, nothing
Now the long story:
I had the ethernet shield working fine on an Arduino nano, with only the minimum connections made with jump wires. When I migrated to a Arduino Mega 2560 (I needed more RAM), and mounted the shield over, I couldn't flash it anymore. I did read the forums and the like, but I wasn't sure which capacitor to remove, nor the manual reset trick worked for me.
So, in a short motorcycle ride, I realized that the shield worked on the nano without the reset connected. Thus I removed that pin and start uploading sketches happily.
Good luck!