Solved.
After spending some hours reading several posts here, I learned a way to fix this and I wanted to share it to others.
a) First of all, yes, it has something related to PHP Version. Once I upgraded some ongoing sites (that I’m currently working on) to V 7.0, an error appears on screen : max_upload_filesize too small on PHP.ini.
b) So I check several sites to change the values for PHP Ver 7.0 and found out that max_upload_filesize was set to 2M. Changed that value to 32M.
c) Also, because this demo uses slider revolution, some other values need to be modified on PHP.ini, such as post_max_size = 8M, that has to be increased to 32, and memory_limit = 128M, increased to 256M.
With all those changes, extended demo content uploaded fine… partially. Now I have the demo content upladed except for the revolution slider (and yes, I had previously installed Slider Revolution and activated the pluggin), because on the website this message appears on top of the home screen : "Revolution Slider Error: Slider with alias church-home not found. "
Because of the several times that I tryied to upload the content, I had four home pages, four Posts, etc. So i decided to uninstall WordPress and start with a fresh and clean installation from scratch. Same result, no slider was being uploaded with the theme. Erased everything (again!) and choosed another extended demo content. All extended demo data, except the slider revolution was properly installed. Anyway I was going to remove that and use another Rev Slider, so it doesn’t affect me at all.
hope this helps.