I have just come across an issue while doing a firmware upgrade with the Cisco mobility express platform on the 1852i access point.

Mobility express allows smaller companies to start to leverage some of the rich features that Cisco has to offer at the fraction of the price by installing a centralised model.   When I mean Centralised I mean having a dedicated appliance in the network to manage all of the access points inside your network.

Where mobility express does not need a dedicated appliance to control the access points inside the network because Cisco have installed a virtual Wireless LAN Controller direct on the access point.

Updating the controller is quite simple.  you can do this from the CLI or direct on the web GUI itself.  I found recently while doing the upgrade from version 8.2 to 8.6 you just need to update the firmware of the code from the Cisco Website and reboot (the steps have a bit more to it but I simplified).  Moving from the code I used a tftp server and used the GUI and CLI to do this, everything copied fine and the AP rebooted BUT still loaded the old code.  There was no errors in the logs to identify the fault.

Thinking about several faults in the past I reduce the codes that I was jumping from at the time so I completed 8.2 to 8.5 with the same issue.  then tried 8.2 to 8.3, this WORKED.   so upgrading from 8.2 to 8.6 i had to do to 8.3 first then I was able to go to 8.6.

If you do have any issues updating the firmware for this platform I hope this information can be useful to helping fix the issue!!