This happened to me last week and I also heard of another guy it happened to as well. I have a 2004 CRF 450R and am miticulous to the point of being anal on bike maintenance. ie changing oil every two rides and filter every ride no matter what. My bike only has about 80 hrs on it of cross country riding if that. And what's weird is the day it happened, I had fresh everything in it(oil, filter). Now the maintenace bill is going to kill me. Honda Canad said it was from lack of oil, but that is a cop out. I've been riding for twenty years and have never had a problem with having the proper amount of oil.