You need to reinstall the .NET framework because of an installation error or another issue.
You only need to follow these steps if you're running Windows 7. The .NET framework cannot be modified in Windows 8 and is not included in Windows 10.
1. Close any software applications you have running. If necessary, use the Windows Task Manager to shut down any programs that refuse to close.
2. Open your Control Panel, and select either Add or Remove Programs or Programs and Features.
3. Scroll down to and click the Microsoft .NET Framework 4 Extended entry.
4. Click Change/Uninstall, Remove, or Repair (depending on the available option).
5. A Setup Wizard will launch. Select Repair, then click Next.
6. The Wizard will repair and, if necessary, reinstall the .NET framework.
7. Important: Restart your computer.