I came across this last week, and thought others might have the same problem.
If you have IE 11 installed, you may run into a problem running Windows update on Windows 7; specifically KB3058515 will fail to install.
The solution is to remove IE (use Control Panel / Programs and Features / View Installed Updates – scroll down until you find Internet Explorer, double click and answer “Yes” to uninstall).
When it has been removed, go to the IE website and download IE 11 (http://windows.microsoft.com/en-IE/internet-explorer/download-ie). Install it, and then the Windows updates should work as normal..