Glad to hear that fixed your problem. Plugs can get sooty if you're starting the bike and taking it for short rides that don't allow the engine to come up to operating temp. Also happens to those that occasionally start up an unused bike and let it idle for awhile before shutting down (not a good practice for other reasons).
When cold, the fuel injection is pumping extra fuel to enrich the mixture (like the old time choke function). The rich mixture will cause soot to accumulate on the plugs until the combustion temperatures get hot enough to burn off the soot. Unfortunately, once a plug accumulates enough soot to keep it from firing properly, the combustion temps will never get high enough to burn it off.
Fortunately, the solution is easy. Ride, ride, ride!
Edit : If you give those old plugs a good cleaning, you should be able to use them again.