http://www.ubnt.com/downloads/XN-fw-internal/5.1-beta/XM.v5.1-beta.3207.091120.1938.bin

Changelog:

* Full legacy product support
* WEP and WPA-TKIP support
* Added: Advanced Ethernet Settings
* WEB server change
* Auto ACK improvement
* Update PPPoE version, port fixes from legacy products
* Ethernet driver update
* AirMax improvements
---AirMax 4 level mac address based priority
---AirMax Automatic Voice packet recognition and TXQ assignment
* MAJOR: Stability issue on link when Airmax is disabled
* MAJOR: PPPoE Stability in HT40 mode (PPPoE session disconnects due to the no response to 5 echo-requests (HT40 mode)
* MAJOR: Fixed performance issue in noisy condition (Rate control algorithm is too aggressive in noisy conditions)
* MAJOR: Fixed WPA/WPA2 client connection issue to
* UI improvements

Known issues/restrictions:
- 5MHz channel width is not available in 5GHz mode (removed until it's stable)
- Channel Shifting in 2.4GHz mode is not compatibile with existing 802.11a/b/g products due to enhancements.
- MCS14/15 does not work with WPA/WPA2 and WPA/WPA2-TKIP (removed from WEB UI) (limitation from Atheros)