X11 focus follow mouse with gimp

Hi Thanks to Yves, the Gimp is now installed but the focus don't follow the mouse. I've installed the "Turn on X11 Focus follows mouse" supplied with Gimp.app but it quits right after being launched and has no effect. more embarrassing, the Gimp crashes, when I brush (it paints a little bit and then crashes). If I can't fix this, I'll carry on using the Gimp in Ubuntu, I'm just fed up with rebooting every ten minutes Any Ideas ? Rémi.