Try disabling you AV/IS suite and any other "realtime" security, such as Windows Defender, MBAM or SAS Pro prior to updating. As a rule of thumb, it's best to do this anyway.
There's also a System Readiness tool to prepare your computer for SP1. Here are the details, it's for the 32 bit version of Windows 7, but there's a 64 bit tool, the 1st one down from "What others are downloading", on down the page.