When I try to backup my sets, they disappear from harddrive!

[frankovich]

Ok, I bought a new comp to run live, everything was going well, I transferred Live over no problem. Now this is where the problems begin, I attempted to backup the whole Ableton folder(containing all my sets) from My documents to a disc. The disc burnt fine, but then when I went to load all my sets on the new computer, about 40 of my latest sets are completely missing from the disc! This had happened to me in the past, so I made sure I did not format the old computer before the sets transferred succesfully.
Naturally I went to the old comp to try back them up again, but to my surprise the 40 odd sets were missing from there also!!!
This cannot be my error as it has happened to me before. I used Nero 7 to backup the folder.
Pleeeeaaaase can somebody help me?????? I have just gained employment as a music producer based on these very sets. They will not be impressed if I have lost them.
How can the act of backing files up cause them to simply disappear???