Burned files are 0 Kilobytes in size..why?

I recently purchased a Plextor PX-708A DVD burner from newegg. It came with Roxio Easy Cd Creator v 6.0 and a few other programs which I haven’t used. I downloaded the latest firmare version for my burner, which is v 1.6 I tried burning some files on a DVD+R Memorex 4x Cd’s. So far, I have 2 coasters. I am trying to back up some files I have, which are in mpeg, wmv, mpg, and avi file format respectively. I have followed the Roxio tutorial to the letter, and it when I go to burn my items it shows no error messages at all. However, when I go to open the files on the recently burned DVD-R+ disc, I notice two things: the file size is zero kilobytes and I get a message from Windows Media Player that tells me there is an error reading from the CD-ROM. Just out of curiousity I tried burning some other files on my hard drive. These movie files consisted of mpg’s and avi’s and yet there was no problem. I don’t understand why the particular files I keep trying to burn come out with a file size of zero kilobytes.Lastly, as I am not sure if this is related to the problem, is the storage issue. The space left on the disc is 3.2 MB as I didn’t want to waste storage capacity. I am also not sure if this could affect my media outcome. Any ideas or solutions are greatly appreciated.