To perform a Factory Reset using either USB Operations or the command line, the "lock" file must not exist. The intent of this file is to make it more difficult to perform a Factory Reset without the owners approval.
The lock file, if it exists, resides in the /home/pi/.est directory, and is simply named "lock". The full path is /home/pi/.est/lock. It is owned by root and must be removed with sudo credentials.
EST Units owned by an Athena for Clubs account by default have a lock file. EST Units owned by Athena at Home accounts do not, be default, have a lock file.