Basically that error pops up when you have textures in the "Element Material" section that haven't been assigned an actual texture (the error is really for saving a texture when someone has been using the painting tool, but the program doesn't take that in to account when it's just "blank").

Most ...

So i have made a block with multiple textures, and i want to get the UV Map so i can use it in mcreator but i cant find a way to get it. Can any one help me?

So i just got this program thinking, oh im gonna have a great time making barrels for minecraft oh? Then i get this error message saying "Your model uses an unsaved texture. To proceed, cubik studio exported it as PNG beside JSON. Move it in tour Resourcepack and update the json if necessary."
So it ...