Not enough information to go on here. What type of disks are you using? Give us the mid codes on them, and the make and model of your burner.
You can find the mid code by using Nero DiscSpeed (free), and click on the Disc Info tab. http://www.cdspeed2000.com/
Are you using the converter program to burn the disks? Is there a log file for the failed burns?
If you are converting avi to dvd format, then I suggest using a better tool. ConvertXtoDVD is popular around here, and there are at least a couple of good free ones as well, DVDFlick and FAVC.
I also suggest learning to use ImgBurn to burn your dvds. There are complete guides at the imgburn.com forums. It is another highly recommended free tool.