I'm using Arduino Uno R3 and the official Arduino WiFi Shield R3. I'm trying to update the Shield's firmware to 1.1.0 through this guide.
Everything goes fine until Step 9. When I execute the code in Step 10, I get an error (see attachment) as:
AtLibUsbDfu: 3EB 2FF8 no device present
FAIL Could not open USB device.
EDIT: I re-installed the firmware on my shield and now the problem's gone.