IDVD burning issues

I have completed my Imovie and "share" with idvd. Sometimes it burns a disc but often times it spits it back out. Then once it does burn a disc, it will not allow another to be burnt without spitting it out. Sometimes I start all over by opening my Imovie project, sharing it with IDVD, and burning- sometimes it works but usually it spits it out.
I am using Verbatim DVD-R 4.7GB 16x 120min Discs... They are brand new.
Using a MacBook Pro (not the unibody) with Leopard
Any thoughts?

additionally I also went and set up a DVD studio pro project and used the disk utility to burn- no luck on that either- spit the disc back out at me