In theory, if you have trouble then just repower the Netduino by detaching and reattaching its USB cable.
If there's a scenario where the 4.2 firmware is causing a Netduino to get into an invalid state, we would love a repro case. The new WinUSB drivers require changes to a few "old ways of doing things" but they shouldn't get Netduino into an invalid state.
Thank you for posting about this. I'm glad it's working for you now. If you have any other troubles, please let us know!
Chris
Chris, as Nak said, what appears to happen is that if, after you have flashed to the new firmware, you attempt to edit the network settings while you are in "tinyCLR" mode (of course, you won't be successful), then you repower the N+ while holding down the button to get to "tinybooter"mode, It will now stay in that mode until you reflash the firmware. Cycling power has no effect. As long as you don't try to change those network settings while in the "tinyCLR" mode, everything works correctly.
I got ahead of myself the first time and forgot that I had to go through the "hold the button" step to reset the network stuff, or I wouldn't have seen the issue.
Bryan