Being sunny weekend today, with full of energy I began to work on making some prototype application which I have to present to my client sometimes during next week. It been a while since I worked on ASP.NET on my application (@ 2 weeks) since I installed Sharepoint Server 2010 demo in my machine. So, with having no idea of a monster under the bed, I made a simple web app and fired it up to debug … and with my little surprise, I got really weird “Page Not Found” error !!! To be honest, I have not seen this error before until today. And I had no idea that what went wrong with it. But I thought that may be it is because something is blocking up my access of application to web server. I checked with my new firewall software (Online Armor) which I had installed few weeks ago for testing purposes (yah, I love testing everything … 
) …
So, I tried to disable the firewall to see if anything happens but still I was getting same ol’ error. So, I again went for help to Google, and found that it can be due to many many reasons … which made me gave me idea to look at my HOSTS file. And while looking at it, I realized that I had installed loopback adapter which had some IP and it was resolving it as Localhost. But the standard 127.0.0.1 as commented out, and I thought may be my application is not being blocked but ASP.NET development server was not able to resolve the DNS !! And once is un-commented that 127.0.0.1 , it stated to work just like before ….
So, in the end I think there could be number of reasons why you can get, PAGE NOT FOUND error while DEBUGGING ASP.NET Application. Some steps you can do it,
Firstly, check you HOSTS file and make sure nothing is wrong with it. (e.g. “127.0.0.1 Loclhost” is commented ?)
Secondly, may want to check your firewall settings !! (if you are using 3rd party firewall chances are high)
Thirdly, check you virus or malware ?? (see this official MSFT Link, they are explaining the reasons and solutions for this)
Some other tests … if you are using IIS, then be sure that you have sufficient rights to do that you want to do…. Be sure that your n/w firewall is not blocking it (can be solved by adding http://localhost to trusted sites ??) … Also, some people are talking about making sure that IIS is configured to use Windows Authentication (I really don’t understand this solution.)
Anyways, for me its finally working … and I guess I will enjoy this weekend with some quality time of coding 
That’s it for now…
It’s just a Thought … 
