Did you try it on other PCs/Macs?
What blank disks are you using? Many problems are a result of the blank disks.
Is it possible to create a image file with roxio on a mac? If so, you might want to try that and then burn the image with the disk utility which came with the mac. I don't know too much about plextors with macs or roxio, but I have burnt many cd/dvds with the disk utility using image files.