I have a nexus 10 that just updated to 4.3,NMI was working fine yesterday,as always, but after the update the cards I was importing yesterday are now not working and coming up as protected.
My wife has just checked on her Nexus 7 and it still works on that so I'm assuming 4.3 has broken it.
I had that happen on my N7G2. To fix it, I opened NMI manually, then I Powered Off the tablet. (Press and Hold Power until you see "Power Off"...) Basically, I followed my own troubleshooting guide.
http://nexususb.blogspot.com/2012/08/trouble-shooting.html