Today a friend of mine called me, and asked me to help him with a problem he was having.

I soon learned that he has an ASP.NET application set up on Windows Server 2003, but he couldn't get the application to load in the browser. Anytime he tried it would always give him a "404 File Not Found" error.

We checked all the usual suspects: IIS running, ASP.NET installed, Web site and virtual directory set up and configured correctly, permissions, checked for a App_Offline.htm file, and so on.

Everything looked good, and we still couldn't see the page. I thought this was odd, we should be seeing something. I then decided to try viewing some static items like images, and some html pages that we in the Web site as well. Wow, these would actually come through fine every time. For some reason, ASP.NET just didn't like us.

I have to admit, I didn't see the answer at this point and I turned to the Web. It took some considerable search-fu, but after a little while I was able to find the source of our troubles.

By default Windows Server 2003 has a security policy enabled that prevents Active Server Pages from running.

Here's all you need to do if you ever run into this:

Open IIS manager, and check Web Service Extension folder, make sure ASP.NET extension is listed and marked as "Allowed".