How to Repair the Windows Update Installer in Vista

Install and Run CheckSUR
1. Log onto Windows with administrative rights. Click "Start." Type "cmd" into the search field at the bottom of the "Start" menu. Click "cmd.exe" to open the command prompt.
2. Type "reg add HKLM\COMPONENTS /v StoreCorruptTimeStamp /t REG_SZ /d “0″ /f" into the command prompt. Press "Enter."
3. Type "reg delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\CheckSUR\" into the command prompt. Press "Enter."
4. Download the System Update Readiness Tool from the Microsoft Download Center. Click "Run" or "Open" to launch the install wizard. Follow the onscreen instructions to install and run the tool.
5. Restart the computer after the System Update Readiness Tool has finished checking the system for errors. Relaunch Windows Update following the restart.
Register Wintrust.dll
6. Log onto Windows as an administrator. Click "Start." Type "cmd" into the search field. Click "cmd.exe."
7. Type "regsvr32 Wintrust.dll /s" into the command prompt. Press "Enter."
8. Exit from the command prompt. Relaunch Windows Update, and attempt to download and install the latest patches for the computer.