Impossible to add media

Hi,

We have a problem to upload media. No any prob if insert with url.
example: https://hpics.li/020558f (sorry it is in french but I am sure you ll figure out).
I can’t find problem similar on the forum (or I havnt found it).

– WordPress v 3.9 (impossible to upgrade to 4.0… same problem?)
– Plugin:

wp security (deleted but we had a a lot of trouble with it)
Jetpack, seo yoast, contact form 7… Other very usual plugins.

Thanks,

Stéphane.