Q: iTunes unknown error -50

iTunes: Advanced iTunes Store troubleshooting - http://support.apple.com/kb/TS3297 > Specific Conditions and Alert Messages: (Mac OS X / Windows) - includes list of iTunes error codes

err = -50 when downloading from store - https://discussions.apple.com/thread/3697501 - delete incomplete downloads from downloads folder as per http://support.apple.com/kb/TS3297

iTunes Store: "Error (-50)" when downloading purchased content - http://support.apple.com/kb/TS1583