I've recently upgraded to WP 3.7.1.
Since then, when I add a media in a new article, the media library is empty, and when I try to upload a new media, I have an error saying that an error occured in the upload of the media.
It seems that there is a problem with either the owner of the files or the file permissions, but I can't change it using my Filezilla.
Every time I try to change to 755, it doesn't work.
See the link of my most recent files in Filezilla :
However, the file uploaded is there (but I can't see it using filezilla) :
How can I solve this problem ?