Have you got the original master key?
Cant really do much without it I am afriad. This is a case for trickle chargers everywhere. Over winter invest in a trickle charger.
Your bike CDI thinks that someone is trying to nick it and so the CDI is stopping the Spark getting to the bike.
You will need master key or new CDI alas. A piaggio garage MAY be able to decode but I doubt it. Get a non standard one dont bother with a Piaggio one these are expensive.
bb
March 2010