As you can see I'm using Anaconda, and in that python environment v. 3.6.6. Just run "import matplotlib.pyplot" the application "breaks". I have searched in StackOverflow anglosajon, but nothing useful. I think it's about version problems.
I have managed to solve it. It occurred to me to update the matplotlib via anaconda to version 2.2.3. Then run the simple "import matplotlib.pyplot" command, and now, no error appears. Even I find it strange that just because it is not so old version crashed.