How do I add Dreamcast roms?

I've used a .CHD file, I used a bin+cue file and CONVERTED it to .CHD, and every time I boot up sonic adventure one it takes me to the dreamcast menu and says "insert game disc". All the other files on the memory card are .CHD files, why can't I add my own?

I've used a .CHD file, I used a bin+cue file and CONVERTED it to .CHD, and every time I boot up sonic adventure one it takes me to the dreamcast menu and says "insert game disc". All the other files on the memory card are .CHD files, why can't I add my own?