Just seen another similar fault on another forum, they suspect the clutch switch, this is a cut-out to stop the bike starting in gear. If this switch sticks you won't be able to start the bike.
To check this wait until the bike won't start again then pull in the clutch lever 3 or 4 times and then try to start. Pulling in the clutch lever should unstick it. You could of course try cleaning this switch.
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Ride on !
