maps created with 1.5 bug with 1.6

Hello,

So i' ve made 12 big maps of my world, spent a LOT of time to do it. I did it with mc 1.5 and now when I launch the 1.6.2 my maps stay empty and nothing appears even when I am on it. I've these maps on frame, in a chest and in my inventory and none seems to work.
It work again when I come back on 1.5...

Please help