Except as provided in subsection (b) of this section, interest shall be paid on a refund claim under § 14-907 or § 14-908 of this subtitle at the rate of 6% a year on the amount of the refund from the date that the tax was paid. Interest may not be paid on a refund claim based on a mistake or error that is attributable only to the claimant and not to the Department, a clerk of the court, or the Director of Finance in Prince George’s County. Interest shall be paid on a refund claim under § 14-906(a)(2) of this subtitle as provided by § 14-608 of this title.