Should I add FSDT Live Update to my antivirus exceptions?
It should be enough to exclude the whole Addon Manager folder, which is our usual suggestion. However, from your report, it seems it wasn't enough so, maybe, it's not just the antivirus, but also a firewall, which might block the Live Update for some reason.
Or it might be another additional antivirus you might running. Some users don't realize they have two antivirus running at the same time and, in addition to the obvious performance issues, there's the added complication of having to manage both (exclusions, etc.)