If the control file doesn't download correctly, save the text to a file with this name.
Hint: The control file specifies the AP firmware image filename and byte count. (you can make your own control files if you have the AP image files)
And view your AP's support info file and examine radio Athstats info. You might have interference on your radio (2.4g/n only). Rebooting your AP will allow it to check and choose the best channel *at that time. *Without a ZoneDirector to help tell APs which is best, you can only rely on the channel chosen when APs reboot (SmartSelect).