Oh my god... this "fix" you asked me to do completely emptied my recycling bin. I *NEVER* empty my recycling bin! When I delete stuff, I use Shift-Delete 95% of the time. I see my recycling bin as a sort of big temporary/backup folder. I did see the command "[Empty Temp Folders]", but how could I even think this would empty my recycling bin :'(
As for Kerio, I did try it in the past and didn't like it, so I uninstalled it shortly after. The OST log specifies "Kernel | On_Demand | Stopped" meaning that the service is stopped. Still, I wanted to completely remove it, so I went in my services and searched for it. I couldn't find it, but I was surprised to find "Windows7Firewall" still running, a free firewall I used while ZoneAlarm was still not compatible with Windows 7, but I only disabled (not uninstalled) when I installed ZoneAlarm. I stopped the service and the updates now work.
Strange though. I've been using ZoneAlarm for the last 2 months and Windows7Firewall was not interfering with outbound connections. Why was it suddenly blocking Avast and not any of the other internet applications I've been using during the last two months?!
Anyhow, thanks for spending all this time with me (us?). You were helpful... even though I lost everything in my recycling bin!