First of all: what we tell about CDs is also valid or quite similar for DVDs.

Working with CDs asks for some special attention.

If you have a CD-writer, then you will have special software to be able to write to your CDs. In most cases however, this software is not compatible to Windows Explorer and is it impossible to copy or write to the CD like you would write to another drive like a hard disk, ZIP disk or Yazz disk. Also if you try to save a file (from a Microsoft office program like Word for instance) then it would not work.
Now, we have the same problem with SmartDirCopy.
However, there is a solution! There exists some CD writing software which makes standard software compatible to CDs. It is, among others, DirectCD from Roxio. DirectCD is a way to write files directly to a CD-Recordable (CD-R) or CD-ReWritable (CD-RW) disc much like you would to a floppy diskette or removable drive. It kind of changes the formats of the CD and with DirectCD itself in memory you can use also SmartDirCopy!

• Writing to CD-R/DVD-R
  We do not recommend writing to non re-writable media. But here some info anyway. CD-Rs are relatively cheap but when removing files, the space is not released. This is a big disadvantage. But if the total size of the source files are small in comparison with the CD-size, then SmartDirCopy can be used. Do not forget to select the kind of drive as CD-R in project edit as precalculation of future free size takes this into account!
  Note that theoretically it is possible to delete files on CD-R in such a way that they are invisible BUT space does not come free. This is why there is chosen not to clean on destination CD-R. So the cleaning phase during backup does not exist for CDRs.
  
• Writing to CD-RW/DVD-RW
  CD-RWs are more expensive than CD-Rs but are still cheap in comparison with many other media types AND they can act like a floppy disc with a huge size! We recommend however to use at least VERSION 2.0 of DirectCD if you write to CD-RWs. If you use a lower version then the CD will most probably be seen as a CD-R and so keep in mind then to select the CD-RW as a CD-R in the project as there won't become space available on the CD when a file is deleted.
  DirectCD 2.0, CD-RWs and SmartDirCopy make up a good team to do your backups!
  If you consider copying a lot and/or huge files then you can think about DVDs. We recommend using InCD (from Nero) for backups to DVD-RW.
• File name compatibility
  CDs in general are not 100% compatible with Windows. For instance if you try to copy files with very long file names (longer than 127 characters) using DirectCD then it could cause errors or even could cause your system to hang. Also some characters are not supported on CDs which Windows Explorer sometimes admit. Many copying programs, including Windows Explorer can fail in such cases. Also problems with SmartDirCopy did occur, notwithstanding the fact we told not to use very long file names. We understand however that sometimes it is hard to prevent such file names and from v1.7 of SmartDirCopy onwards we built in some special protection against this: long file names can be automatically cut on the CD + some forbidden characters (very rare though) are ignored. So certainly consider our file-name-checking feature when editing projects if you copy to other destinations than usual hard disk!
  
  Remark that it is possible that EMPTY directories which should be removed during cleaning phase are possibly not removed from the CD-RW. A warning will be given in normal report so that you can eventually remove them manually if you really should want to.

For download and further details on DirectCD, please search on Roxio. There are versions for both CD's and DVD's. For DVD-RW try Nero.