Just got the ProTools Duet and I have the same problem.
Tried different USB-ports, cables, even Macs. No solution.
Apparently, Apogee made a working version for the firmware updater just last month.
http://www.apogeedigital.com/support/duet-ios-mac
Avid last updated the drivers in January. I really hope they will incorporate Apogee's update in their version of the drivers soon.