I looked at the threads that you posted, and saw that you apparently tried to remove / reinstall, you checked to see if any 3rd party firewalls weren't blocking any Avast services, and that you have correct registry settings for the Windows Temp folder.
In the removal process of Avast 4.8 (Which I assume you were using before upgrading to 5), did you remove through Add / Remove programs, then reboot into safe mode and run the removal tool for 4.8?
Did you just upgrade directly to 5 without uninstalling the previous version?
Have you attempted to completely remove avast 5, reboot into safe mode, use the removal tool for 5, then reboot and install from scratch?
If you've done all of that, then I can assume we can rule out an installation problem. The problem is that I haven't had any of these problems with my Avast 5 installations (only about 5 so far) and I'm not sure where to start troubleshooting further. All I know is that clean installations usually fix the most common problems like these.
If my post doesn't help in any way, hopefully someone else with more insight can help you soon.