When you encounter an error like Error Code : 0x80070021;

HTTP Error 500.19 - Internal Server Error. The requested page cannot be accessed because the related configuration data for the page is invalid.

Follow the steps as shown below to fix this problem:

  1. Open the Server Manager interface
  2. Select Features from the left menu. Click Add Features
  3. In the Select Features interface, expand .NET Framework 3.5.1 Features
  4. Select the check box next to .NET Framework 3.5.1. Click Next
  5. Click Install in the Confirmation page. You will see the installation progress
  6. Click Close to close the wizard once the framework has been installed