So I've had this issue for a couple of days, several tries at reinstalling the update. Then I ran CHKDSK to try and fix it, even tried clean boot mode nothing has worked. I've attached a CBS log to see if someone can spot the issue.
(reference Security Update for Windows 7 for x64-based Systems (KB2868626)
(reference Security Update for Windows 7 for x64-based Systems (KB2868626)