You cannot convert .mds file (Alcohol 120% disk image descriptors) to DiscJuggler image format (.cdi). For a successful conversion, you would also need a corresponding .mdf file that actually contains the disk image which is needed for the conversion. So a lone .mds file is useless to you for conversion purposes.
This conversion entry was verified by us and conversion was flagged as wrong or not possible.
Usually this happens when the conversion would try to convert different types of data between each other, such as audio to image, or it is not possible because incompatibility between programs, caused by closed file formats, very limited support etc.
If you find entry that you feel is flagged as bad wrongly, please tell us in the discussion below with as much as information as possible so we can fix it.