It's very common to have a error happen when burning cdroms.
When burning from linux it's always a good idea to compare the md5sums of your downloads and your finished disk.
Usually the md5sum is given to you in a form of a text file on the server were you downloaded the cdrom images. If your making a copy from a known good disk then you can get the md5sums off of that.
For example you download a iso image. You find he md5sums for the disks...
Then you run:
md5sum ramdumb.iso
and that spits out a number, it should match the indicated text file.
Then after you burn the image you can, if your using Linux or whatnot, but not in windows, use md5sum to check the cdrom image:
(the device names will differ from distro to distro)
md5sum /dev/cdrom
and that should match the md5sums from the original image.
That way you can be 95% certain that it's burnt correctly. Otherwise rates for successfully burning disks, especially 4 or more of them for a installation, is around 50-90% depending on the cdrom burner and how well the machine is set up.
If your using windows you can use the md5sum.exe program, but I don't know a easy way to verify a disk after it's been burnt.