aspnet_regiis -i

Use the following commands to either register for the first time or re-register your ASP.NET with IIS.

For ASP.NET version 1.1.4322:
C:\WINDOWS\Microsoft.NET\Framework\v1.1.4322>aspnet_regiis -i

For ASP.NET version 2.0.50727:
C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727>aspnet_regiis -i