Okay.

I now have this.

- launch LC_MESSAGES=C LANG=C xmms ; sleep 2 ; xmmsctrl main 0 play_list 1 play
plus exec xmmsctrl next
minus exec xmmsctrl previous
fullscreen exec xmmsctrl pause

Everything works (previous song/next song) when the screen is locked but it doesn't play any songs.

What simple thing did we miss on this?