Thanks for your help MiSAKACHi. It pointed me on the right direction. Actually, I'm using a remote dedicated server on a hosting provider on which I don't have access. But the
<RSWindowsBasic/> is there as it can load the report with PHP 5.4. Everything is fine under this version.
Thanks to you, I found the issue : I'm using HTTPS and with HTTPS it doesn't work whereas it works when I'm using HTTP ! I'm check with my hosting provider if they can do something.
EDIT - Solution
My hosting provider fixed the issue last year (forgot to post it here). During the time it wasn't fixed, I was still under PHP 5.4. I paste their original message :
These issues that you describe is because the installed Certificate is a self signed Certificate. New Web Browsers and PHP Version don't accept these Certificates because of Security Risks.
We have changed the Certificate with a official issued Certificate