It would seem the power for the shield should come from the sanguino like it does from the arduino. You may be creating a power loop by providing your own supply.by Franklin - Controllers
That's the way I've gotten it to work for me (resetting while downloading) but it only works about 40 percent of the time and is a real pain. On mine the green led glows weakly if the power switch is in the ext position, is that normal?by Franklin - Controllers