Persistent (null)_GENERIC_ERROR_MAC_TEXT when resetting MacBook Pro

I'm getting this error: (null)_GENERIC_ERROR_MAC_TEXT when trying to reset one of our MacBook Pros. The employee left years ago but obviously signed in using a now deactivated email address. I recreated the email in Google, which we use to authenticate, but the error persists.

[Re-Titled by Moderator]