Hello Bill,
Internet Information Services need to have the .NET-related features checked in the Windows Features dialog box as shown below:

Besides that, these features need to be registered. This is done with the tool aspnet_regiis.exe, which should be installed in the .NET Framework directory. For more information check this MSDN article: ASP.NET Integration with IIS 7.
If you still have troubles installing Telerik Report Server, please open a support ticket and let us help you.
Regards,
Ivan Hristov
Progress Telerik
Progress is here for your business, like always.
Read more about the measures we are taking to ensure business continuity and help fight the COVID-19 pandemic.
Our thoughts here at Progress are with those affected by the outbreak.