oprion - that's very strange that airodump-ng doesn't work. You definately seem to be typing the right command.

Just as a matter of interest, if you type ifconfig does wlan0 show up?

airodump-ng on the N800 is a little flakey anyway - I think because of driver issues you tend to get phantom APs as well as real ones showing up, and it will sometimes misdiagnose WEP protected APs as WPA2 etc etc. I don't know if the same is true on a N770