http://social.msdn.microsoft.com/Forums/en/vssetup/thread/1172440a-a354-4f5c-8431-b2a854e1d761
1.start - run - key in "cmd" and enter - key in "net stop WuAuServ" and enter
2.start - run - key in "%windir%" and enter - find the folder named "SoftwareDistribution" in the open window, and rename it "SDold"
3.start - run - key in "cmd" and enter - key in "net start WuAuServ" and enter
4.start - run - key in "regedit" and enter - find the sub-key "MAIN" of "HKEY_LOCAL_MACHINE\SOFWARE\Microsoft\Internet Explorer" and right-click on, then click the menu "Permissions",and then the "totally control" to be "permited"
And then you may install Microsoft .NET Framework 4 successfully.