Upgrade Virtual Controllers firmware a second time via GUI or CLI:
You can perform the following from the VC AP using the CLI (Command Line Interface/SSH with PuTTy). A TFTP or FTP server will be required and there are many freeware TFTP/FTP servers available on the Internet:
device-upgrade load-image ap7522 tftp://<hostname|IP>[:port]/path/file [enter]
or you can use FTP:
device-upgrade load-image ap7522 ftp://<user>:<passwd>@<hostname|IP>[:port]/path/file [enter]
Once file has been uploaded successfully to the VC AP, have the customer reload (reboot) the non-VC APs and they should upgrade from the VC AP.