Invalid or Unsupported File Format in ImgBurn

I am using ImgBurn for burning Blu-Ray video disks. It has support for CDI images but not for multi-session images. Is this the reason why I am getting an “Invalid or unsupported image file format” error when I try to load an image from Dreamcast? If so, what do I need to resolve it? Please help.
ImgBurn
Invalid or unsupported image file format!
OK
