Your welcome.
I think it may be relevant, with spybot trying to do a scan on the next boot there may wel be some possible conflict with avast, which does a limited scan on boot. The additional activity by spybot trying to open files to be scanned would cause avast to also scan that file before it allows spybot to scan it.
Personally I would leave that option well and truly alone based on your findings the problem isn't there when you don't select that option.
Using windows explorer navigate to those folders and check the file/s exists, it is just confirming they exist as missing files could cause a failure to load a device, possibly the S32 EVNTI.DLL.
I would most certainly recommend using the site and removal tool to ensure you have no Norton remnants, it can really get its hooks into a system and cause all sorts of issues even when uninstalled. The tech probably did an uninstall but not the extra step (not always required) but you still have the Symantec folder.
As to what version of Norton you have, I can't tell you how to find that out, but you could take an educated guess based on when the tech installed avast NAV works in years so if it was two years ago you may have had NAV 2005 or NAV 2004, depending on how long ago and how long you had NAV.
I also did a google search for S32EVNTI.DLL and that shows it is a Symantec virtual device driver so if that was missing it would fail to load.
http://www.google.com/search?q=S32EVNTI.DLLSo there would appear to be a registry entry trying to load this device driver file.