How to audit group membership changes?

How to audit group membership changes?

Hi guys
 
I'm having some problems auditing group membership changes. I have Win 2008 Active Directory. In my domain controller policy I have set up Audit Account Management to Succes/Failure but I can't get it to audit changes?
 
I have read the articles below:
http://www.shariqsheikh.com/blog/index.php/201103/auditing-group-membership-changes/
http://whatevernetworks.com/?p=21
 
Any Ideas what I am doing wrong?
 
Brgds
Liselotte