A .rar file is a compressed archive. "21006" often appears in specific contexts:

: The official tool for .rar files. You can download it from the WinRAR Official Site.

: This usually means the download was interrupted. Try deleting the session and downloading again.

: Ensure your hard drive has enough space. If your PC memory is exhausted, the file may not extract fully.

Right-click the file and select or "Extract to 21006/" .