This error (The system cannot find the file specified) belongs to µTorrent and it occurs when a file downloaded by µTorrent is not available. This mostly happens when Anti-Virus deletes a downloaded file due to file’s suspicious pattern.
If you try to start downloading again, it fails with another error “Error: Files missing from job. Please recheck”.
To fix this problem, right click at the name of torrent and select “Force Re-Check”.