Well the strange thing is that the windows file system error 0 = the operation completed successfully. So this is a little strange.
If you have had a previous installation it would probably be best to do a clean install.
- Download the latest version of avast pro, 5.0.545 (presumably this is the one you have)
http://files.avast.com/iavs5x/setup_av_pro.exe and save it to your HDD, somewhere you can find it again (if you didn't save your last download). Use that when you reinstall.
- Download the avast! Uninstall Utility, aswClear5.exe
find it here and save it to your HDD (it has uninstall tools for both 4.8 and 5.0).
- 1. Now uninstall (using add remove programs, if you can't do that start from the next step), reboot.
- 2. run the avast! Uninstall Utility from safe mode, first for 4.8 if previously installed and then for 5.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.