Using an animated gif
directly as a source is not possible. Try the approach that is described in this thread: Using an animated gif as a displacement map - shaders
An alternative is the mentioned approach with a single (PNG) image that contains all frames of the animation.
More information about this topic here: http://www.html5gamedevs.com/topic/10299-animated-gif-image-as-texture-how-i-can-use-it/