Microsoft CRM 4.0 installation ASP.NET 2.0 is not installed
Try reregistering ASP.NET v2.0.50727 by running the below line from a command prompt.
C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis.exe -i â€“enable
Microsoft CRM 4.0 installer checks for a specific filter that is removed after .Net Framework v4 is installed.
In IIS Manager, right click Web Sites, and select Properties.
Under ISAPI Filters you will see the below
Add a new filter you call "ASP.NET_2.0.50727", pointing to C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\aspnet_filter.dll.
Dynamics CRM should now install without issue.