BuddyPress.org

It might be your url for the background. You might need to start further back than the img folder. In order for mine to work I used

url(/www/wp-content/themes/themename/img/header.jpg)

I’m using transmit on a mac, and I can right click on the .jpg to see the properties and copy the path. Not really sure about this, I’m knee deep in creating my first child theme myself, but it’s worth a shot.