Something is up with Google I believe. I have the same problem. I have Adsense on several sites and they all get traffic but when I go to Adsense it says 'no data.' I never received an email about any violation and have committed none. Also, there are no messages in my account saying there are any problems. This happened just before I was to meet my payment threshhold (hmmmm).
I tried repeatedly contacting Google about this and no one has responded. Anyone ever have and resolve this issue?