It seems like .nbf and .nbs files were both created by NTI Backup Now! software, however in different versions or for different purposes. It is unlikely you could somehow convert one to another.
In order to recover your files, you will probably need the exact version of the program that created your backup.
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.