With my dedicated Windows 2003/IIS 6.0 server I want to run latest version of .NET framework on it. Hence I use my Web Platform Installer to install .NET 4.0. Everything goes smooth. It was piece of cake to install it.

Now the time came to run my first .NET 4.0 Framework application, I configure a New website in IIS. Select .NET framework 4.0 from ASP.NET tab in Website property. But what I found is I am getting 404 error. Strangely enough that Default.aspx page does exists and with .NET 2.0 it works just fine. So what goes wrong ? I search and experiment with web.config, but to no avail.

Then I found this article http://www.denalimultimedia.com/info/Articles.aspx?cid=20&topic=IIS-6-ASP-NET-4-0-page-not-found-404, which clearly mention that

• Install framework asp.net 4.0 and restart [Web Platform Installer does it just fine]
• IIS 6.0 console should now display ASP.NET 4.0 under tab “ASP.NET” [It was again done if #1 above is right]
• Under Web Services Extensions (in IIS console) .NET 4.0 framework might be set as: prohibited. This must be ALLOWED otherwise a browser might just return the error 404 page not found which is not very descriptive
• ASP.NET 4.0 applications must be run in a separate process (Application Pool) otherwise you’ll get the error ‘Server Application Unavailable’.

It is anyways always good to run different programming languages in different pool. For Example, if you want to run PHP on same server I use different pool for them. Covering those 4 steps I got my server working with .NET 4.0. Wondering why Web Platform Team forgot to complete 2 step in their installer.