Sorry to bring this old topic up…

One partition is now C:, and there has been no problems anymore. Even the e-mail scanning works now! Now i am waiting for a virus database update to be 100 % sure that it was the missing C: that caused the problems - i am not reinstalling, if the first update does not use the regular auto-update mechanics (compare to the manual updating, which works).

Is there others who do not have C: drive? It might help to find out if this problem is actually caused by Avast.