Baking multires displacement map problems.

Hi i’m relatively new to blender, just started using it last month, but i’ve gotten the hang of it through all the great tutorials.

My question is that how come when i try to bake my displacement map to a blank uv grid, nothing happens. I have my multires modifier on with the preview set to the highest level. The funny thing though is that i have already done this and it worked! But for some reason when i press bake, i wait for the process to finish, only to find that the map is still black as if nothing happened.

Could you please give some answer because i’ve searched everywhere and no one else seems to have the same problem.

If you need pictures just ask.