Another data point. We've had a similar issue a couple of times in the in the last year. Bugs, dust - something seems to collect at the ignitor point keeping the system from igniting. My cure has been to use a nozzle on my air compressor and blow air into the system during the ignition sequence. I did a fairly detailed write up if you want to try the fix I used. Here is a link:
http://www.thorforums.com/forums/f8/...ted-10346.html