There can be several reasons, here are some things to check.
The file your are trying to burn is corrupt in some way, or is too large for the disk.
The CD's you are using are not 100% compatible with your burner, try a different brand or type.
The CD's are simply from a bad batch, it happens, and most of the time when an error is encountered, its the fault of the disk itself.
Burn at a slower rate.