my chankast sucks

(i'm french sorry for my bad english.)
i have instaled chankast alpha and chankast ex in my computer and downloaded dreamcast bios, aspi force, a virtual cd drive software, 2 utopia boot disk and some dreamcast cdi games. but when i mount utopia boot disk and i start chankast, it doesnt work. Chankast detects the utopia disk like it's a audio disk. why?
(one of my utopia boot disk is a nrg format and the other is a cdi format.)
please help me.

try NullDC, haven't got Chankast to work yet either. Lots of people haven't