Hi whoslooking,
I tried your 5.1.6 firmware for downgrading my 5.2.0 cameras and it works perfectly.
Now the version is: "V5.1.6 build 140412" so it seems to be April 2014 build.
Here: http://www.cam-it.org/index.php?topic=8148.msg48578#msg48578
I read: "Also, make sure you use the June 2014...