Blender black UV map problem

[Gatto Spingflower]

hello people, i have this issue...

i create a sculpty and start to model it,then i save the blend file to keep working later,then what happened wen i opened the file next day, the uv map was showed all black!!! ive tryed to look on the image tab list to see if there but is not, they are all black. i also tryed to switch betwen modes, select and deselct, etc etc but is no use.this always happens wen i save the file to continue later and open it.

any sugestions?

Thanks.