Can you tell us a little more about your system.
What Operating System are you using? is it up to date?
What avast! version and VPS file (virus database) number, e.g. 0436-4 (see about avast!)
How long have you had avast installed ?
Do (or did) you have another AV installed, if so what (and how did you get rid of it) ?
Have you tried a forums search for SI: 0x00000005, etc. this returns many hits, do any of them match your circumstances ?