This is the second time I receive this message from Google. Last year, a post from Philipp Lenssen's Google Blogoscoped made Google change its mind. Thanks to Matt Cutts and other Googlers, I got this reply:
"While we do require that publishers obtain permission before running AdSense ads on Blogger sites that contain Google Trademarks in the URL, we've re-reviewed your site and are happy to grant you permission to continue running ads on googlesystem.blogspot.com."
This week, Google disabled the ads again, for the same reasons as before, but this time I didn't receive any reply from Google. It's strange to see this if you think that Google Operating System has never mislead people into thinking it's an official Google blog and the usage of "Google" in a subdomain should be allowed: "Don't register Google trademarks as second-level domain names," says one of the many Google guidelines. There are many important sites that use "Google" as part of the subdomain or domain name and Google still serves ads for these sites. What's more, I received permission to run ads on this blog.
Update (13 hours later).