Urgent - Visual Studio 2013 Debugger Returns Null for Request.ServerVariables["Logon_User"] during Debug

Hi,

Just started using Visual Studio 2013 and an developing on an old website I have been developing for a while. Now that I am on VS2013, when I run the debugger, Request.ServerVariables["Logon_User"] returns a null value in debug. In production everything works fine but I am not able to debug the code during development. I have       <authentication mode="Windows"/> in the web.config in both environments. 

The development machine is not part of a domain and I expected to get MachineName/UserName in the response. Any ideas?

Thanks.