The backup of a course download with 0 bytes.

I backup a course and when I try to download it, it downloads with 0 bytes

However, other courses download well.

I see the course that has been backed up but there is no way to download it. 

I can restore it in the same moodle site but I can't download it to restore it in another moodle installation because it downloads with 0 bytes. Is there any way to locate it in moodledata?

Some idea,

Thank you.