If you install the .NET Framework on a system that has IIS already installed, IIS is automatically configured to handle requests to ASP.NET pages, and to redirect the execution to the ASP.NET runtime. However, it may happen that you installed the framework on a Windows 2000 Professional system where IIS was not already present, and just later decided to add IIS. Registering ASP.NET on IIS is not just a matter of associating the various .aspx, .asmx, .axd, .ashx and the other ASP.NET extensions to the aspnet_isapi.dll ISAPI, more has to be done to create the ASP.NET account and to set it for ASP.NET requests, register the ISAPI itself and other stuff. Doing all this manually can be a difficult operation, and requires a good understanding of many details. Fortunately there is an utility, shipped with the .NET Framework but not documented, that can take care of these configuration chores for you. The utility is aspnet_regiis.exe, it is located under %WindowsDir%Microsoft.NETFrameworkvx.y.zzzz and you should call it with the -i parameter: aspnet_regiis.exe -i