Thank you for the solution it works fine !
But there is a new issue ^^ The visual I want to project on the ground is animated, and by just adding the "projected texture" flag it stacks all the "frame" of the animation, so the animation is not played anymore.
Is there something specific to do in order to keep the animation of the projected texture, is it even possible to do this in wotlk ? because I don't see any "projected texture" spell visual that have an animation in wotlk