Possibly:
1. Invalid clicks. Do you have competitors that want to put you out of business? Check your logs.
2. You have some .com names listed in your keywords. This could also be construed as "tricking the search engines." Why put other domain names in your keywords? And if these aren't your domains but domain names that belong to competitors, doing invalid clicks may be their revenge on you.
3. Your navigation links are at the footer: highly inconvenient for readers to find. Maybe they'll click an Adsense ad first? Google Adsense may not like this. You're supposed to build a site for readers, not for Adsense.

Please heed the advice above to not depend on one income source. No business can be built on this and you see the result of it. And finally: "Live by Google, die by Google."