"Folder cannot be found" ... are you sure it doesn't say "File cannot be found"?
probably means that the file has been moved or renamed or deleted outside of Lightroom. To fix this problem, see: Adobe Lightroom - Find moved or missing files and folders
thanks so much, I tried but could not find he files; are these collections, 1.0 thru 5.0, meant to be teaching tools? Perhaps they are available for downloading somewhere on the Adobe site
Use your operating system search function to search all of your hard disks, to see if the files are still on your hard disks somewhere.
I don't know what those collections are or where they come from.