The estimated size of the project is larger than the default space available
There may not be enough space available on your disc to burn your project.
You can use the Optimize Disc dialog to fine-tune your recompression settings or use the Project Overview window to delete assets from the project.
The Target media size (GB) drop-down list on the Disc Properties tab of the Project Properties dialog determines the amount of space the application uses to calculate the space available on the disc.