Welcome to discussions, DD:
It is more than likely just a media error.
Change the DVD Brnad (most folks around here suggest Verbatim DVD-R 4X) and burn it as slowly as possible. 1X or 2X if you can. Save the DVD project as a disk image and use the disk utility or Toast™ to burn it:
(Thanks to Len Goff for the copy & paste here):
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File/Save as Disc Image...
http://docs.info.apple.com/article.html?artnum=164927
This will isolate any encoding/burning issues you may encounter. Once the disc image is created, double-click the .img and burn the virtual disc that should appear on your desktop, using Toast to burn the DVD. Disk Utility to burn the .img file. Usually, you can select a burning speed in Disk Utility.
There are variations to this process based on which OS X you are using...
Open Disk Utility (in Utilities folder in Applications folder), click on the virtual disc (maybe the .img) in the left-hand window. Click the Burn icon. A new window should drop down and your SuperDrive tray will open after clicking the Burn icon. Insert a recordable DVD. (Verbatim DVD-R preferred by me.) Click the Close button. Wait. Select a burn speed. If you hold your mouse cursor over the pop-up it says: "Select a slower speed to work around burn failures," so select 4x or slower for best results. Then click the Burn button.
-->If the virtual disk selection won't allow you to click the Burn icon, use the .img file instead. This may have changed in 10.3.9 and did change in Tiger.
Also, you can use DVD Player to play the virtual disk to check your iDVD project before burning to DVD. Launch DVD Player. File/Open VIDEO_TS (Open DVD Media... in Player 4.6). Find the VIDEO_TS folder and open that. (The audio folder is for DVD-Audio disks.)
http://docs.info.apple.com/article.html?artnum=93006
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Sue