Coursepress File Download Error: file is empty

Hi guys!

I created a File Download element in a course. It's a 13MB file.

When a student try to download the file, he gets an error: the file is empty. If I test the file URL, it works. But inside the unit, the error occurs.

Here's a screenshot of the unit.

I don't know what is causing this error. I tested in localhost and everything works fine.