Whilst you can export C4D images to JPEG, the opposite conversion is most likely not possible. You may be able to import JPG to Cinema 4D, but you probably cannot simply "resave" it as C4D.
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.