Using 802.11n here with D-Link gear. Just thoguht I'd mention it for anyone else who is having the same problem, it only connects at 54mb/s unless you are using WPA or WPA2 as well as AES. It was driving me mad all week until I managed to stumble upon the solution. Nothing online seems to say this (not that I found anyway) so figured I'd put it up.
Hope this helps.
Maz