Had exact same problem and its actually quite easy to fix. Switch off electrical power at mains and cut power at fuse box for safety first of all. Then unscrew then oven unit from housing and remove. On top panel of oven remove screws (approx 6). Lift up the panel and to the left is a small red reset switch, press it to reset. Replace lid and screws and rehouse oven - its as simple as that!
Pat
November 2009