It is unlikely that you could somewhat manage to convert ARC backups to NBF. Both are backups from Nokia phones, but each of them was created for different purpose. At best you can find a utility that can extract the data from such backup but conversion is most likely not possible and wouldn't even make sense.
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.