Most of what I have read about he vista/update error 80070490 says that a repair installation is required to fix the issue. Another suggestion that you might want to try yourself is to manually download and install windows updates, then reboot and retry automatic updates. Some of the suggestions mentioned that the issue may have been caused by malware, and that the malware was unable to be cleaned with current versions of av/anti-malware applications. The sollutions suggested where malware was a concern was to perform a complete re-installation, including reformatting the disk.