802.11a/n

[Grant]

I'm using a Ubiquiti SR71-E 802.11abgn card and I've tried specifying
many different channels for 802.11a mode but I always get this error:

wlan0: IEEE 802.11 Configured channel (36) not found from the channel
list of current mode (2) IEEE 802.11a
wlan0: IEEE 802.11 Hardware does not support configured channel

Also, it seems strange to specify both hw_mode=g (for example) and
ieee80211n=1.  Is that the correct config for 802.11n?

- Grant