Problem With new blank dvd-r

I bought a 50 pack of Sony dvd r 4.7 mb. I have been burning movies to them with no problem until about 20 disks in and now they are showing space already taken up and telling me not enough disk space to burn the movie. Any solutions?
 
I'm not entirely convinced it's the discs. At least not yet. It could be the computer or burner. Have you tried the offending discs on another machine? Have you tried them in another machine BEFORE inserting them into this particular computer?
 
Back