Unifi controller 2.x.x. was on an SBS 2003 server controlling 5 APs
we upgraded it to 3.xx and then to 4.6.6 and backed up the config to a thumb drive. Disconnected the SBS box.
replaced the sbs 2003 with an essentials 2012R2. Installed 4.6.6. controller on that box. loaded configuration. it lists the APs as adoption failed.
I went into each details / advanced options , entered username / password as ubnt / ubnt clicked adopt. still adoption failed.
I found this page:
ran the script in PS (PS opened as admin).
repeasted the adoption steps and still adoption failed.
turned off windows firewall, repeast adoption steps, still adoption failed.
the APs have solid green lights.
I had already power cycled them (pulled injector AC power for 15 seconds, then reconnected AC power.)