I had a similar problem with my MacPro while using OS10.6. It turned out my DVD/CD burner was the problem. I had the unit replaced (it was covered by the Apple Protection Plan) and the problem went away.
Well my apple care plan is expired as of last august. So im kinda looking for a fix other then 400$ for to renew my apple care considering im a student who doent work more then 15 hours a week.
The firmware on Apple's built-in drives is very picky about media especially when using Toast to burn discs. I suggest getting some Verbatim-brand discs and give those a try. Also set the burn speed at something slower than Best such as 4X. If you are using Toast 10.0.5 then download Toast 10.0.4 from Roxio's software updates page to see if that helps fix the problem.
Im using memorex and it had been using them just fine until about 2 months ago. And it let me burn one dvd this morning on said disc then it was like "nope not doing it" by getting the same error.