Oh, @simon, I love you!! I didn’t related the problem with this settings because the error was recently, and I touched there at the installation beginning, a month or so ago. I suppose I don’t visit this pages (TOS, FAQ…) usually enough!
Thank you very much!
In any case, I think is not very clear the explanation you can found below the little window where you can enter that values. At leas, in spanish. See:
It says like: If you have a document for (privacy p., tos or faq) hosted anywhere, put its URL here… But, isn’t it better to add “but leave it empty if this URL is at your Discourse installation” or something like that? I assume that, writing this few letters more, It would be clearer for other clumsy guys -or girls- like me in the future… 
Is an idea… Thanks! Gracias!