I've known this on a variety of vehicles that have been left for a long time with the handbrake engaged. The cure, unless you can de-adjust the shoes, is a bit harsh and can be scary. With your handbrake lever off, attempt to drive forwards and backwards sharply. Make sure no one is in front or behind the vehicle when you do this. It may take a few go's and there will be a load bang when the brakes release. I have never known any damage caused by this method and the brakes have always been working ok afterwards. If in doubt, strip them down and clean them up remembering to copper-slip the metal to metal contact points.
Kevin, December 2005