Download keeps failing. + Error message.

[ghost]

[youtube:playlist] Downloading playlist PLRDHCw-CyvDzm-nc - add --no-playlist to just download video swqbfMh467A
[youtube:playlist] RDHCw-CyvDzm-nc: Downloading Youtube mix
Traceback (most recent call last):
File "/usr/bin/youtube-dl", line 6, in
youtube_dl.main()
File "/usr/lib/python2.7/dist-packages/youtube_dl/init.py", line 804, in main
_real_main(argv)
File "/usr/lib/python2.7/dist-packages/youtube_dl/init.py", line 794, in _real_main
retcode = ydl.download(all_urls)
File "/usr/lib/python2.7/dist-packages/youtube_dl/YoutubeDL.py", line 982, in download
self.extract_info(url)
File "/usr/lib/python2.7/dist-packages/youtube_dl/YoutubeDL.py", line 493, in extract_info
ie_result = ie.extract(url)
File "/usr/lib/python2.7/dist-packages/youtube_dl/extractor/common.py", line 158, in extract
return self._real_extract(url)
File "/usr/lib/python2.7/dist-packages/youtube_dl/extractor/youtube.py", line 1490, in _real_extract
return self._extract_mix(playlist_id)
File "/usr/lib/python2.7/dist-packages/youtube_dl/extractor/youtube.py", line 1464, in _extract_mix
title = clean_html(title_span)
File "/usr/lib/python2.7/dist-packages/youtube_dl/utils.py", line 403, in clean_html
html = html.replace('\n', ' ')
AttributeError: 'NoneType' object has no attribute 'replace'

[jaimeMF]

Please post the full output you get when running youtube-dl THE_URL --verbose.

[ghost]

[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['-t', 'https://www.youtube.com/watch?v=swqbfMh467A&list=RDHCw-CyvDzm-nc&index=7', '--verbose']
[debug] Encodings: locale 'UTF-8', fs 'UTF-8', out 'UTF-8', pref: 'UTF-8'
[debug] youtube-dl version 2014.02.17
[debug] Python version 2.7.6 - Linux-3.13.0-30-generic-x86_64-with-Ubuntu-14.04-trusty
[debug] Proxy map: {}
[youtube:playlist] Downloading playlist PLRDHCw-CyvDzm-nc - add --no-playlist to just download video swqbfMh467A
[youtube:playlist] RDHCw-CyvDzm-nc: Downloading Youtube mix
Traceback (most recent call last):
File "/usr/bin/youtube-dl", line 6, in
youtube_dl.main()
File "/usr/lib/python2.7/dist-packages/youtube_dl/init.py", line 804, in main
_real_main(argv)
File "/usr/lib/python2.7/dist-packages/youtube_dl/init.py", line 794, in _real_main
retcode = ydl.download(all_urls)
File "/usr/lib/python2.7/dist-packages/youtube_dl/YoutubeDL.py", line 982, in download
self.extract_info(url)
File "/usr/lib/python2.7/dist-packages/youtube_dl/YoutubeDL.py", line 493, in extract_info
ie_result = ie.extract(url)
File "/usr/lib/python2.7/dist-packages/youtube_dl/extractor/common.py", line 158, in extract
return self._real_extract(url)
File "/usr/lib/python2.7/dist-packages/youtube_dl/extractor/youtube.py", line 1490, in _real_extract
return self._extract_mix(playlist_id)
File "/usr/lib/python2.7/dist-packages/youtube_dl/extractor/youtube.py", line 1464, in _extract_mix
title = clean_html(title_span)
File "/usr/lib/python2.7/dist-packages/youtube_dl/utils.py", line 403, in clean_html
html = html.replace('\n', ' ')
AttributeError: 'NoneType' object has no attribute 'replace'

[jaimeMF]

You are using an outdated version (quite old), it works fine in the last version. Run sudo youtube-dl -U to upgrade.
If you still have the problem with the last version, post the verbose output and I'll reopen the issue.