Site is PHP, there is no .htaccess file, and the ads all show up perfectly on every page. Nothing wrong. But it won't validate: says it didn't find ads on the home page. They are clearly there. No frames or anything weird. What else can I check for?
I changed the DNS as you suggested, and it's had several days to propagate now - but it still won't validate. Anything else I can try? (I tried listing it by IP address but it looks like the site doesn't have its own unique IP.)
Still wrong... you need to use name servers that actually are valid name servers for your domain. Or at the very least name servers that are not the same as the validation server.
This was finally fixed by moving the site to a different ISP. Had something to do with the DNS. Hope this helps someone...