I don't know why you dug this ancient thread.This thread is from 2008 year.Some people have realy archaeological capacity LOL.
This error have many various options and there is no easy answer,each case is individual.
First I suggest to run sfc tool and readiness tool and don't be lazy and want to view what is CheckSur.log and in SFC report.Even you have any corruptions in CBS,WinSxS in mostly cases Readiness Tool can't fix them automatically and there is no such kind of tool -you have to do that manually
If there are some errors in SFC report and in CheckSur.log you have to analyze and fix them manually,if there are not errors than probably any 3p programs disturb installation.
In this case you could try install updates/service packs from Microsoft Download Center,reset Windows Updates or rid of program which cause problem -of course always is problem to guess which one it is Krunk4Ever! » Blog Archive » Windows Update Error: 80070490 - After eliminating all other possibilities, the one remaining-no matter how unlikely-must be the truth.
apart 3p sucurity software also other programs may cause problems e.g Deamon Tools,Alcohol 120,USB Safely Remove and probably many others (check also user comments not only main article) +wide google of course
There is also special MS fix which could help you if you have no errors in SFC report and CheckSur.log and still you have no clue what cause your problem Error message when you install an update by using Windows Update on a computer that is running Windows Vista or Windows Server 2008: "0x80070490"
Sometimes you have to analyze full CBS log (not only SFC report) How to overcome error 0x80070490 when installing updates in Windows Vista/Server 2008 - Andreas Klein - Site Home - MSDN Blogs
I have only one objection to @andrekl post:
His reset.bat script does not restore original permissions but give much more permissions for Users and Administrators than they have defaultly -this fix has been created for XP but in Vista default permissions are completely different,much more subtle and for security you shouldn't apply this - if you really suspect issue with permissions you should
-uninstall all 3p security software
-try both tools to verify permissions
1)MS Fix It-> How do I restore security settings to the default settings?
2)Rizone Security Restore http://www.rizone3.com/?download=secres.zip
-If really nothing help:use Process Monitor to diagnose issues with permissions