I have exactly the same problem on a 2000 model estate. Ford want minimum of £450 just to try to sort it. Looking at the web tonight, it seems a common problem. I believe on mine water has managed to get into the solonoid and locked it up. I have spent over 4 hours trying to get the door off already... They seem impenitrable, but once the door is off, there looks hope. I may resort to cutting the door out as a second hand door is around £ 50. Quite a saving in comparison... Good luck!
DJ
January 2008