It sounds like the previous owner failed to pay a maintenance bill incurred just before he sold you the plane! What a nice guy, if this is true! By the time the lien was filed, the airplane was already legally in your possesion, while the public records still showed the previous owner as owner of record. It often takes some time before such records are updated.
Did you order the FAA CD containing the aircraft's records before you bought the plane? The revoked airworthiness would have shown up then, but the lien wouldn't have, as it hadn't been filed yet. Your buyer might have ordered the current CD, and if he backs out of the deal (likely) he might sell or give it to you. They don't cost much, anyway.
The N number registration actually has little to do with the airworthiness certificate, similar to the way a car's license plate and registration has little to do with a state inspection roadworthiness sticker. Homebuilders routinely register their airplanes before the Airworthiness Certificate is issued before first flight.
You're not the first that this has happened to! I don't know exactly what you need to do, but I'd start by talking to an FAA FSDO rep, as the FAA will definately be involved in the solution. You need to find out from the FAA why the airworthiness was revoked. That's the biggest problem! FAA involvement means fixing the problem is likely going to take at least a few weeks. Are you a member of AOPA? Call them and ask for help and advice. I'm sure they've seen this before as well. Another source of information and possible help is your state DOD. Almost every state has an aviation branch of the DOD, and I'll bet they even have a website. I know Florida does, and I'm on a first name basis with Bo, as I've called him so often for advise. They may be able to intervene on your behalf and ask the repair shop to withdraw the lien, as you're not involved in the debt. It is also possible the bill HAS already been paid, and the lien was not cleared as it should have been.
There is a solution to this problem! It may take a while, and your sale is likely lost, but it will all work out!
