HelloCustomerand welcome to just answer.
They are not releasing your refund due to the outstanding balance you have from 2006. Even if the balance is not due til May 22, 2008, they will not release your refund until the balance has been cleared up. You may also find that you may not receive your stimulus payment until the balance is cleared up from the IRS.
Since the IRS examined your 2006 taxes and found some items that they are rebuttling, The the state still needs to recalculate you prior state return to see if thier is a balance due to them as well. If you have not yet heard from the state, you may want to amend your state tax return and send it in to the state for 2006. This will help speed up and refund that may be due back from the state.