Both MKV and MK3D are the same Matroska container, albeit used for different purposes. A .mk3d file is meant to contain 3D video, whilst .mkv files are the "normal" Matroska Videos. You probably cannot just convert one to another, because 3D movies needs to be recorded that way and cannot be just created from normal ones.
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.
