Hi, having the same problem here. The Pi 3 seems to be very picky when it comes to SD cards/ images. I can burn an OSPI image to an SD card and run it in a PI2 with no problem. Place it in the PI3 and nothing. Take the same SD card and reformat it with SDFormater and install Raspian on it and it will work in PI2 and PI3. Manually install OSPI on the same card and it will run on both PI2 and PI3. Make an image of that card using Win32DiskImager, reformat the card and burn the image and it works fine on PI2 but nothing on PI3. I have tried many cards of many makes and sizes. Overall the results are the same, although there are a couple of cards that PI3 won’t boot from at all, but PI2 does.
If I create an image from a card that has a “modified” system on it e.g. tightvnc, ftp enabled etc, the image will boot so I am confident that the image writer is working OK.
So in a nutshell, I can’t create an SD card from an image that has OSPI on it.
Barry