Same problem here.
- Clean install of Windows 7
- Only a few apps installed for media center (show analyzer, dvrms toolkit)
- No other virus software ever on this build
- Running Windows firewall
- Happy AVG client on Vista, decided to try Avast on media center and WHS server
- Downloaded / installed Avast! free for Win7 v5.0.418.0
- Worked fine for a few days, then got same errors described above (won't start, "file system shield provider not found")
Tried the "repair" route as recommended in threads, but didn't work. Doesn't seem to me that reinstalling the app is much of a solution, though I will try it once before reverting to AVG Free. LMK if you want any diagnostic data.
Thanks,
Mike