Files like this often require a password found on the original download page. Never download "password unlockers" for these files, as those are almost always malicious.
To help you further, could you tell me or what you were trying to download (e.g., a specific game or software)? bnsDA.part20.rar
If this was downloaded from a peer-to-peer (P2P) site or an unofficial forum, it may contain malware or adware . Files like this often require a password found