1) Start Parallells and run your OS of choice; 2) Plug in the USB device; 3) From Parallels, select the device for the list at the bottom right for the screen; 4) See the error message? Okay then try the following: - Open a Terminal and type the following four commands to unload the drivers marking the device "in use" (even though OS X doesn't know what to do with it): sudo kextunload -b com.apple.driver.AppleUSBCDC sudo kextunload -b com.apple.driver.AppleUSBCDCWCM sudo kextunload -b com.apple.driver.AppleUSBCDCACMData sudo kextunload -b com.apple.driver.AppleUSBCDCACMControl (Note: this is a non destructive action and the drivers will be loaded *again* next time you plug in any USB device). 5) From Parallels, select the device from the list at the bottom right of the screen again and, this time, everything should work normally (assuming the proper drivers have been installed, etc.) Hope this helps! K.