I upgraded my Mountaineer Eth board to firmware 4.2 QFE2 and strictly followed the instructions on upgrading the USB driver to the WinUsb version as documented (see http://www.mountaineer.org/app/download/6122023375/Mountaineer+Firmware+and+USB+Driver+Installation+Guide+for+NETMF+4.2+QFE2+V20120921.pdf).
I just want to add that the USB driver upgrade process should be done for each USB port where the Mountainer Eth board is connected to.
I found that after upgrading the USB driver and verifying that the driver details correctly show “Service=WinUsb”, a bluescreen happened again when pressing the RESET button. In my understanding this shouldn’t happen with the WinUsb driver (user mode). I found that I plugged the board into a different USB port. The driver details showed “Service=PortUsb” for this port. I had to change the driver manually to “WinUsb” following the documentation.