1. The disc must be single-session and the disc must be closed - click "Write CD" instead of "Write Session" when prompted by Toast to accomplish this
2.The device you intend to read the disk in must be compatible with the media and format you are using. To determine this, you may want to contact the manufacturer of the drive. In most cases, you will have better luck with CD-R/DVD-R than with CD-RW/DVD-RW media.
3. For more information on Recordable vs. Rewritable media see the following URLs:
www.cdrfaq.org

http://www.cdrfaq.org/faq01.html#S1-1
http://www.cdrfaq.org/faq01.html#S1-7

http://www.cdrfaq.org/faq02.html#S2-12

http://www.cdrfaq.org/faq02.html#S2-13