To access the content within sone206u.part03.rar , you cannot simply extract that single file. Multi-part archives work sequentially. Steps to Extract:
If "sone206upart03rar" refers to a part of a series (possibly a manga, anime, or software), you might find it on torrent sites. Be aware that downloading copyrighted material without permission is illegal in many jurisdictions.
This usually means one of the parts (perhaps part 03) was corrupted during the download. Try redownloading the specific part that is corrupted.