I have looked through the forum and could not find a relevant solution for this. This is not an "M" unit. I followed the firmware procedure as described at http://wiki.openwrt.org/toh/ubiquiti/bullet and have found the following (below). I looked for history locations for an older FW version and the latest I could find was from 11/2014 (?) and it produces the same result. I have successfully loaded the DD versions on another unit. This is my alternate test piece and would like to test the OWrt versions. Any assistance would be appreciated.
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BusyBox v1.01 (2013.03.28-08:56+0000) Built-in shell (ash)
Enter 'help' for a list of built-in commands.
XS2.ar2316.v18.104.22.16858.130328.1054# wget -O /tmp/fwupdate.bin "$url"
Connecting to downloads.openwrt.org[22.214.171.124]:80
XS2.ar2316.v126.96.36.19958.130328.1054# /usr/sbin/fwupdate -m
-sh: /usr/sbin/fwupdate: not found
// manual entry to install
XS2.ar2316.v188.8.131.5258.130328.1054# cd /usr
XS2.ar2316.v184.108.40.20658.130328.1054# cd /sbin
XS2.ar2316.v220.127.116.1158.130328.1054# fwupdate -m
Invalid version 'XM.ar7240.v6.0.0-OpenWrt-r43949'
/bin/fwupdate: Firmware update file check failed!