If I have a newer AEC firmware version, "2.1.9.x", can I downgrade it to 220.127.116.11?
While it is possible to downgrade the firmware to this version it is not recommended.
Downgrading to this version will cause all stored AEC usernames and passwords to become unusable. Even the default user1/8088 will not work.
The only option would be to default the entire AEC database and then reload a valid backup of the database.