How do I clear this at the Registry of Motor Vehicles?

If a taxpayer finds him/herself in this situation and has been refused renewal of a registration or license, he/she may remedy the matter by making full payment on the bill, including all fees and penalties, which will include a $20 release fee. Once the bill has been paid, the deputy tax collector will give the motorist a receipt to show the Registry of Motor Vehicles as proof of payment. At this point he or she can reregister the vehicle.

Vehicle owners should be aware  that the excise tax law (M.G.L. c. 60A) gives tax collectors six years from the date a bill is issued to collect an excise tax bill. However, under Registry regulations, tax collectors have two years from the date of issuance of an excise bill to notify the Registry of nonpayment. The Registry will then electronically mark the driver’s record for non-renewal until the excise is paid. If the tax record does indicate a history of nonpayment, the tax collectors can also mark the driver’s record and institute proceedings to collect for as many years back (in other words, beyond six) as necessary.