Lloyd Miller,
Tax Lien is released when the debt owed is paid or if it becomes unenforceable due to time lapses. If the taxpayer has an Offer in Compromise in place or if the outstanding debt is paid in full, the Tax Lien will also be released.
There are a few reasons the IRS may withdraw a Tax Lien before the debt is paid off in full and they are the following:
1. The filing of the notice against the taxpayer was premature or not filed correctly
2. The taxpayer has made an agreement with the IRS to pay back the outstanding debt amount
3. The withdrawal of the notice would allow the taxpayer to pay off the debt
4. The withdrawal would be in the best interests for the taxpayer and the government combined
The following IRS link may also help you with said tax issue:
Tax Liability
Sage