This security update to Silverlight includes fixes outlined in Security update KB3126036. Non-security related changes are also included in this release and have been documented in the Silverlight Release History. This update is backward compatible with web applications built using previous versions of Silverlight.

If you are facing an error while installing or updating the Silverlight then follow the below steps.

Click Start and type Notepad in the Search box.

Double-click on Notepadfrom the list of results above
Copy and then paste the following text into Notepad.
reg delete HKLM\Software\Microsoft\Silverlight /f
reg delete HKEY_CLASSES_ROOT\Installer\Products\D7314F9862C648A4DB8BE2A5B47BE100 /f
reg delete HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\Products\D7314F9862C648A4DB8BE2A5B47BE100 /f
reg delete HKEY_CLASSES_ROOT\TypeLib\{283C8576-0726-4DBC-9609-3F855162009A} /f
reg delete HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\install.exe /f
reg delete HKEY_CLASSES_ROOT\AgControl.AgControl /f
reg delete HKEY_CLASSES_ROOT\AgControl.AgControl.5.1 /f
reg delete HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\{89F4137D-6C26-4A84-BDB8-2E5A4BB71E00} /f
rmdir /s /q “%ProgramFiles%\Microsoft Silverlight”
rmdir /s /q “%ProgramFiles(x86)%\Microsoft Silverlight”

4. Click File and Save As and type CleanSilverlight.cmd
5. In the Save astype box, click All Files (*.*)
6. In the Save in box, click Desktop, and then click Save
7. On the File menu, click Exit
8. Right-click the CleanSilverlight.cmd file on your desktop and click Run as administrator
9. When the uninstall completes, right-click the CleanSilverlight.cmd file on your desktop and click Run as administrator a second time
10. Once the uninstall has completed, click the link below to install the latest version of Microsoft Silverlight.

http://www.microsoft.com/getsilverlight/get-started/install/default.aspx

11. Delete the CleanSilverlight.cmd file from your desktop.