Hi
I figured it out.
When I downloaded the install files I did it twice, and placed them in two folders on my desktop, later I copied one of the sets to my D:\ drive, but I left them on the desktop as well.
This was a total of about 35 gigabytes of data, stored on the desktop.
I finally realized that the reason that I couldn't copy the files organised into different folders from my D:\ drive to the DVDs was because I didn't have enough space left on my C:\ drive (my temporary Windows 8 partition) to allow it to swap the files from one place to another.
I removed the files from the desktop and it copied them fine after that.
Funny though, when I finally did it I put in the DVD dragged the folder to it one by one, watched the copy...