A claim must be disallowed based on the invalidity of the debt before the associated lien can be voided under Section 506(d), the Ninth Circuit ruled in upholding the BAP.
The value of a disputed claim is proven by showing the likely validity of the claim and the likelihood of recovery, not just by establishing the possible damages.
As long as the rate is legal under state law, considerations of equity will not allow a court to disallow default interest to an oversecured creditor under Section 506(b).