Oh my. This was never a LR issue, it was a backup/restore issue. Your first fault was in 5-9. Since you deleted the image files, but LR still had them imported (in its database), LR still knew about the photos, only they weren't there. All you had to do was to restore them, from your backup CD to the drive, in the same place where they were. Then everything would have been back in business. This was not an issue of "missing files" or a need for synchronization or anything to do with LR. It was a matter of deleted files needing a restore from a backup.
Since you now have removed the folders inside LR, it means LR has lost all knowledge of those photos. They are gone from LR's point of view. This should mean that 10 should work, since the images are new from LR point of view. apparently it doesn't work which is strange. However, even if it did work, it would mean that you import those images from scratch, thus loosing any edits you have made to them.
Do you have a backup of LR's catalog file (the database)?