ADL Initialisation Error! Error -21!

[dense]

Hi all,
 
I'm trying to get all of my cards running, 3 of them work fine, but the last one has some issues. I'm using Ubuntu 13.04, AMD 13.12 drivers, SDK 2.8.1, ADL 5.0 and 4x 7970's with CGminer 3.7.2.
Aticonfig --lsa shows all 4 cards fine, but ./cgminer -n only shows 3 and then the ADL Initialisation Error! Error -21! message after it. I run CGminer through a script with DISPLAY=0 and have a dummy plug. Anyone know what's wrong?
 
Thanks!