When trying to downgrade the firmware below 1.04.23 the "Old ADSL firmware!!" message appears and firmware cannot be downgraded even with power off or factory reset.

To downgrade below v1.04.23 ("Old ADSL firmware!!" error):

- Backup and document current configuration
- Factory reset the unit (password: admin)
- Set Device Admin | Remote Upgrade = Enable
- Use TFTP to upload the firmware

Further information can be found at:
http://theether.net/download/NetComm/NB5580W/firmware/readme.txt

Firmware versions can be found at:
http://theether.net/download/NetComm/NB5580W/firmware/