Hi,
If the bike is still on the original plugs it maybe due a change, I had a misfire problem on mine at around 20000 miles (2004 model) which a new set of plugs fixed. Do you know if there is something on the bike that could drain the battery ie an alarm etc, mine struggles if left for a while, I suppose I should get a trickle charger, but after a run it works a treat. Also check that the spark plug caps really are nice and tight esp the inner two as even a small gap can let water in and then you will get running/starting probs.
Cheers
P