To fix IIS mappings for ASP.NET, follow these steps:
Run the Aspnet_regiis.exe utility:
Click Start, and then click Run.
In the Open text box, type cmd, and then press ENTER.
At the command prompt, type the following, and then press ENTER:

“%windir%\Microsoft.NET\Framework\version\aspnet_regiis.exe” -i

In this path, version represents the version number of the .NET Framework that you installed on your server. You must replace this placeholder with the actual version number when you type the command.
Register the Aspnet_isapi.dll:
Click Start, and then click Run.
In the Open text box, type the following, and then press ENTER:

regsvr32 %windir%\Microsoft.NET\Framework\version\aspnet_isapi.dll

Regsvr32 returns the results of the registration.