【求教】关于导出gif动画的问题

mathematica9.0.1，win8
命令是：
FF = Table[
Plot3D[Sin[x^2 + y^2 + a]/(x^2 + y^2 + Abs[a]), {x, -2 Pi,
2 Pi}, {y, -2 Pi, 2 Pi}, PlotRange -> {-1, 1}, Boxed -> False,
Axes -> False], {a, -Pi, Pi, Pi/12}];
ListAnimate[%]
Export["zz.gif", FF]