1. Login to server.
2. Download Microsoft .NET Framework 4 web installer package.
(http://www.microsoft.com/en-in/download/details.aspx?id=17851)
3. Run the web installer file.
4. After completing installation, reboot the server.
5. Login to Plesk panel.
6. Select 'Server components' from 'Tools and settings'
.
7. Select the option 'Refresh components'.