Low disc space as the reason of "Could not copy file" in the process of images uploading

Hello! I had a message "Could not copy file".

First I thought the reason was that just before I added SSL for the domain and redirect to https

and the redirect from

http://h5p.org/sites/all/themes/professional_themec/images/h5p.svg. 

to  https://h5p.org/sites/all/themes/professional_themec/images/h5p.svg 

was set manually.

But later I found out that the reason was in the disc memory space on hosting. 

Adding some memory on hosting resolved the problem.