This has happened to my STS sites as well after editing web components in Front Page. I received the following advice from the TSC Developers at http://sharepoint.ebuscollab.com.
"This issue, more often than not, is due to improperly editing the default SharePoint Team Services pages...
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.