It seems that the installation file for Microsoft .NET Framework have been corrupted. Uninstall the existing versoin, and install an updated one.
Before doing the steps below, do a full registry scan and fix-out the errors. Use RegInOut software for that.
Here are the steps:
1. Click Start -> Control Panel.
2. In case of Windows XP, click "Add or Remove Programs" icon.
In case of Windows Vista/ 7, click Programs -> Uninstall a Program.
3. Select "Microsoft .NET Framework" from the list of installed programs.
4. Click "Uninstall" or "Remove" button.
5. Restart the system after completion.
6. Download a latest version from here:
http://www.microsoft.com/downloads/en/details.aspx?FamilyId=333325fd-ae52-4e35-b531-508d977d32a6&displaylang=en
7. Install it on your computer, and do a reboot after completion
اذا في اي خطوة مش مفهومة ارجو الاشارة اليها.