Another of the strange, unexplained errors with a simple (yet unexpected) cause.
You are developing an ASP.NET Site or Web Project in Visual Studio 2005/2008. You start the Debug process. Your browser window opens with a message:
Page Load Error
The page cannot be found.
Additionally, you have Windows Defender installed on your machine.
A flawed update of the Windows Defender removes the localhost entries from hosts file in windowssystem32devicesetc folder.
Manually add the following entries back to the hosts file:
More details: http://www.h-online.com/security/Windows-Defender-False-alarm-triggered-by-hosts-file–/news/112814