Hi Victor,
I remember an issue with the SecureStacks and similar switches as your G3, where a locked out admin account would not be re-enabled automatically. I have seen this with a B5 some years ago, the GTAC Knowledge site has an article regarding the D2 (
How to recover a D2 when locked out of admin account over time). If I remember correctly, the issue was fixed years ago, you should consider a firmware upgrade.
Workaround was to use the rw account to copy the configuration off the switch, edit it to not include the admin lockout command, copy this edited configuration file to the switch, and reboot with the edited configuration ("configure configs/edited_config").
Erik