I would suggest that you first update the program as 4.8.1296 is an old version, the current one is 4.8.1335.
Try a manual Program Update - right click the avast ‘a’ icon, select Updating, Program Update. The Program update also includes iAVS (VPS) update.
However, your error is somewhat strange as I believe the SI: 0x00000005 is a windows file system error (5) = Access is denied. So it may be better to do a clean reinstall.
Download the latest version of avast http://www.avast.com/eng/download-avast-home.html and save it to your HDD, somewhere you can find it again. Use that when you reinstall. Ensure that you scroll down and select the avast direct download link for the English version and not Cnet as that is for an on-line installation (not what you want to do). - Direct download for avast Home, English version, http://files.avast.com/iavs4pro/setupeng.exe.
Download the avast! Uninstall Utility, find it here and save it to your HDD.
Now uninstall (using add remove programs, if you can’t do that start from the next step), reboot.- 2. run the avast! Uninstall Utility, reboot. If step 1 failed it may be necessary to run this from safe mode, once complete reboot into normal mode.- 3. install the latest version, reboot.