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Fast busy signal means you entered something wrong, or a 'refusal' of what you entered.
If you can access admin settings at all, then either the admin password ***** been changed, or your source for the information you are using is unreliable. Do you have a programmers manual or an administration manual for the Vodavi Starplus STS ? if so, have you identified the model # ***** your Vodavi system box without mistake or question?