Newest version of Avast! 5.0 on my Vista Home Premium 32 Bit machine still has this problem. I remember that all versions 5.0.x I tried had this problem.
It looks like that :
-I uninstall Avast 4.8
- reebot,
- install Avast 5.0.x
- configure password for Avast, so unprivileged users cand modify settings (leaving all checkboxes at default state at password tab)
- everything works perfectly,
- than after one or two reebots (after a day or two) when computer starts avast informs that all shields are down.
- I try to enalble them by :
- using context menu by RMB clicking on Avast icon at tray,
- using shields management screen
- using START->Administration tools->Services and trying to start Avast main service
but with no success - avast tells me that there is some error, so shields can't be reenabled; service starts and in one moment stops.
I noticed that Avast is downloading and installing updates properly (at least by these one or two days).
My system specs (this is computer for my kid):
ABIT KV7 (mainboard)
AMD Sempron 2800+ (Socket A CPU)
Kingston 1,5 GB DDR (RAM)
ATI Radeon 9250 (GPU)
Windows Vista 32 Bit Home Premium.
EDIT :
oh, and one more thing - I'm using Pro version... version 4.8 of Avast works perfectly on this machine