I started debugging one of our sites today after having a new 64 bit virtual machine with Windows 2003 Server installed on it. After setting up all websites, code, etc and when I pressed F5 on my Visual Studio 2008, I got the following error
"Unable to start debugging on the web server. An authentication error occurred while communicating with the web server"
Most of the answers on net point to doing an IISRESET and enabling HTTP Keep-alives, neither of which worked for me. But the following link proved to be useful and after carrying out the steps, it finally start working for me.
Blogging it, as it might be useful for somebody else.