A short guide for troubleshooting Windows Update Agent:
1. Download and execute//install “System Update Readiness Tool (CheckSur)” from https://support.microsoft.com/en-us/kb/947821.
Check the following log for errors C:WindowsLogsCBSCheckSUR.log
2. For any updates that could not be repaired by CheckSur, download the msu-package manually from Microsoft Catalog, http://catalog.update.microsoft.com/v7/site/Home.aspx or from Microsoft Download Center, http://www.microsoft.com/download
3. Create the folder C:WindowsCheckSurpackages if it doesnt already exists and move the downloaded updates there.
4. Execute “System Update Readiness Tool (CheckSur)” again.
5. Install updates from Windows Update.