I routinely get emails stating that my site fails revalidation and I know for certain that ads are displaying and do display from other remote locations. It appears to be a problem with how the revalidate works. Perhaps it queries google and google rejects the request? the exact page is http://www.therenoguide.com usually if I try to revalidate manually it will work. Sometimes I have to wait hours before it will work. Thanks for checking on this.
One possible source of the problem is Google has pages indexed for your URL which no longer exist. If this is the case you need to ask Google to remove non-existant pages from index. Another source for the problem is you have redirects on some of your pages. Good luck, Shannon