I'm having persistent problems with W5100 shields on Dues. Most of the time, they work just fine. But, when I do a firmware upload, the W5100 somehow gets into a state where it seems to be just out to lunch, and nothing short of power-cycling gets it going again. I can repeatedly reset the Due, but the W5100 just sits there with only a single red LED lit. Everything else in the system works as expected, and this is happening on numerous different sets of hardware, so it appears there is something happening in the firmware upload process that puts the W5100 into a state it cannot recover from.
Anyone have any ideas what might be going on, or how to fix it?