Finally! Someone else with my same problem. I have an 09 250 and the gas gauge crapped itself the first long weekend I tried taking it out, under 100 miles at the time. Took it into the dealership and they found out the sensor inside the tank was bad. Replaced it and about a week later (a couple hundred miles put on it, a little over 200) and the gauge was broke again. Took it back in and it was the sensor again. They called Kawasaki. Got back to me and I was told that it's the gas that's ruining the sensors. I'm getting my 3rd one installed this weekend. Apparently its causing corrosion to build up on the sensor which destroys it. When they pulled everything off and let me look in the tank I could see the gunk hanging out at the bottom of the tank, a light brown color. Its the ethanol in the gas. With the emission laws forcing the gas stations to blend this crap into the fuel, they don't measure how much or how little since there is no set standard. I don't go to middle of nowhere gas stations either, I stick with highly traveled ones which usually watch their mixtures (or so I was told).
They shipped off my original sensor to Kawasaki so their engineers could take a look at it. Kawasaki said my bike was the very first case they have ever heard of this happening..