I'm Terribly sorry friend. Thanks for willing to help.
The thing is: I found out what I was doing wrong (and failed to delete the thread). I was trying to sell my metals before filling 100% my refinery (and therefore, not having an actual unit of that metal to sell). Noob stuff.
Now it is solved, I'm getting rich, being able to provide an outsdanding life-style to my 6 wifes and 32 sons.