I had issues with my new nano too until this evening when I downloaded the latest drivers (1.13) and Kontrol Editor (1.20).
As I understand it, If you have moved the nano to another USB port, you have to run the driver installer again, so it installs the driver for that nano to that port.
The only other thing I found out was that, under XP you can “fill up” the number of MIDI slots available in the Windows registry. M-Audio do a tool to clear duplicate driver entries (due to the point above) that sorts this.
