After performing a fresh DNN 7.1.2 installation on today, it would give a 404 error when trying to reach any page.  You’d actually get the page you requested, but then overlying the page was the pop up error message, and it was pointing to:

http://www.customerdomain.com/Getting-Started/mid/363?ReturnUrl=http%3a%2f%2fwww.cocos2dxna.com%2fHome&popUp=true

404 (Not Found) 

The fix for this was found in the DNN forums here:

http://www.dnnsoftware.com/answers/cid/302718/page/1

It was simply adding the portion in red below to the <modules> tag in the web.config.

    <modules runAllManagedModulesForAllRequests="true">