Register ASP.Net 4.0 handler mappings in IIS:
1. Go to the .Net command prompt.
2. aspnet_regiis –i
Install the current version of ASP.NET and updates IIS  configuration at the root level to use this version of ASP.Net.
3. aspnet_regiis –r
Install this version of ASP.NET and update scriptmaps at the IIS metabase root and for all scriptmaps below the root. Existing scriptmaps are upgraded to this version regardless of the original versions.