Problem Landcsape painting

When I Paint the selected layer, this appened. And after that, I can paint in other “regions” but this one stay like that. The red message tell me “GRASS MAPS NEED TO BE REBUILT (1 object)” But I dont know what I have to do with that.
Can anybody help me ?

Hi, do you have all your textures samplers set to “shared wrap”? Otherwise if you use (paint) more than 16 texture samplers (some of them get used under the hood so in practice you have less) you get this grey checkered default material.