Latest upgrade to antiX-13.1 full fixes a bug in the etc/apt/sources.list.d/antix.list (dev was in the repo line and it is now removed- thanks SamK for spotting it). However, youtube-viewer-antix may have got upgraded to the latest version. If you are using stable repos, this will break youtube-viewer.

Simple fix if broken:

apt-get purge youtube-viewer-antix
apt-get update (make sure your antix.list does NOT have dev and debian.list is set to stable/wheezy)
apt-get install youtube-viewer-antix

If you were running antiX with testing repos, youtube-viewer probably broke a while back, but the latest should fix it. It needs perl 5.18