This could happen if at sometime you stopped Windows Updates half way or your PC was shutdown or restarted either due to an error or by mistake. This corrupts the Windows Updates Agent.
To resolve the problem, try deleting the c:\windows\winsxs\pending.xml file as following and then download and install the Windows Update Agent from Microsoft.
1. Click Start – All programs – Accessories, right-click “command prompt” and select “Run as Administrator”.
2. Run the following commands to take ownership:
C:\>takeown /f C:\Windows\w
C:\>cacls C:\Windows\winsxs\pending.xml /G
C:\>cacls C:\Windows\winsxs\pending.xml /G ANNAI\SAI:F
3. Delete pending.xml as follows:
4. Download and install Windows Updates Agent from one of the following:
5. Reboot the computer when prompted. Once restarted, run Windows Update again and that should run smoothly.