1. Did it work with previous versions?
2.There seems to be a problem with that MAC, the OUI database can't find a valid record for it either:
http://standards.ieee.org/cgi-bin/ouisearch?22-E3-1F
Double check your MAC. Those first three digits represent the device manufacturer, and should be registered with OUI. I just tried entering the MAC of one of my devices on the Mac filter, and the webui accepted it.
1. I don't know if Guest MAC Filtering worked with older versions, I only tried it on 155.
2. Very strange... I was using this MAC in the MAC Filter of my old Netgear router and it worked fine. My printer has both LAN and WLAN interfaces, and I just noticed that with MAC Filter disabled and the printer connected (wirelessly), Asus reports the connection MAC as the printer's LAN MAC.
So, I entered LAN MAC into RT-N66U MAC Filter and it seems to work fine. Thanks!