HTTP 404: The page cannot be found. (ASMX or ASPX)

IIS 6+ is setup to return a 404 on executable types that are unrecognized or prohibited. This is the case with both ASP.NET 1.1 and 2.0.

1. Open the "Internet Information Services (IIS) Manager" under "Administrative Tools".
2. Navigate to the "Web Service Extensions" node.
3. Select "ASP.NET v1.1.4322" or "ASP.NET v2.0.50727" in the right pane.
4. Click "Allow".

If you don't see the expected version of ASP.NET listed under "Web Service Extensions", it's typically because IIS was installed after .NET. You can run the aspnet_regiis.exe utility to remedy this:

1. Get to a command prompt, e.g. Start>Run "cmd".
2. Enter "CD /D C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322" or "CD /D C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727" depending on which version of ASP.NET.
3. Enter "aspnet_regiis.exe -i".
4. Wait for the finished message; "Start installing ASP.NET (1.1.4322.0)" or "Start installing ASP.NET (2.0.50727.0)" depending on which version of ASP.NET.
5. Follow the previous set of steps to enabled ASP.NET in Web Service Extensions.