Keep getting this error while trying to update
Okay, as I thought, the error just disappeared for me the next day. So, just be a little patient and it should go away. If it persists, use the manual updates from Apple Inc.'s website.
AntiVirus apps have been known to cause various problems on OS X. Macs are not immune to malware, but no true viruses exist in the wild that can run on Mac OS X, and there never have been any since it was released over 10 years ago. The only malware in the wild that can affect Mac OS X is a handful of trojans, which can be easily avoided by practicing safe computing (see below).I solved this by temporarily disabling my anti-virus/malware product.
I use Kaspersky, which is generally excellent, and performs url inspection.
I still need to dig in to determine why software-update checks in the AppStore app trigger an intercept by Kaspersky.