This is a weird little problem that pops up on some titles for a handful of users when the DVD they try to Clone has a ‘jacket’ folder or ‘Img’ folder.
Some 3rd Party app or windows add on is trying to do something special that temporary causes CloneDVD to loose site of the DVD you have asked it to back up.
The easiest way around this issue is to drag 'n' drop/ Copy the 'VIDEO_TS' folder to the hard drive then start CloneDVD pointing to this new source.
The hard way is to find what is causing this conflict and clear the issue.
I my self do not have any issues backing up my DVD’s that have a jacket or img folder, so I cannot shed any clues on where to start looking, sorry.