The System Volume Information folder is a part of the system restore function and as such is protected by windows, so much will be hidden and also protected from access. That area is where the _Restore points are stored.
Ensure that you have hidden files and folders enabled and disable hide system files in Windows Explorer, Tools, Folder Options, Hidden files and folders, see image.
That still won’t allow access but at least you should be able to see what is there.
avast is able to access them, that KB article is likely to be old and AVs have progressed, avast can certainly move or delete infected _Restore points is that is the action you choose.
Deletion of an infected _Restore point (if that was an action you chose) only deletes that restore point and not ‘all’ restore points, avast doesn’t disable system restore, consequently removing ‘all’ restore points. That is why I asked if it was still enabled, checking if you hadn’t inadvertently disabled it losing all restore points. So it would appear that this was nothing other than a hiccup with system restore.
You now have a clean restore point now which is available as you said, so this is your new start point and if things are working OK then it shouldn’t be an issue.
System Restore is far from perfect which is why I have taken steps (Drive Imaging software) to replace it so I can completely disable it, so I don’t have to rely on it.
There are many, many reasons why a System Restore may fail. For example, see “Why are previous restore points not working?” in the “Troubleshooting” section of this official Microsoft page:
http://www.microsoft.com/technet/prodtechnol/winxppro/plan/faqsrwxp.mspx
There’s lots more on that page that’s worth reading too. Note especially the sections on “Does System Restore protect personal data files?” (the short answer: no); “What should I do if System Restore does not work?”; “Why are my restore points missing or deleted?”; “Why does the System Restore Wizard lockup?”; and so on. Just a few minutes on that page ought to convince just about anyone that System Restore is not intended for heavy-duty system protection!
More info:
http://www.kellys-korner-xp.com/xp_restore.htm
http://www.google.com/search?q=system+restore+fail