Players blocked and black screen after several hours in a net with a proxy

I have installed 1 server Xibo 1.7.8 under Windows 7 pro and 6 players 1.7.8 under Windows 7 pro in network in remote agencies. The network uses a proxy. In the starting up, everything was very well, but at the end of 24 hours, the next morning and all other mornings since then, certain machines are blocked on a video or an image, and others have a black screen, with obligation of reboot to leave on all these machines. Some other work, but the reliability is random. Players turns 24 hours a day.
For vidéos, I’m using K-Lite, with program Windows Media Classic.
For browser, I’m using Firefox
After I changed for Internet Explorer and Windows Media or VLC but always the same error.
For information, all the machines are new.
The serveur is an intel core I5, a motherboard Z97 gaming 3 socket 1150, ram 8 gigas, under Windows 7 professional and players are PC gigabyte Brix GB BACE 3000, Intel celeron N3000, ram 4 gigas, under windows7 pro also.
Can you help me please.
In the log of players, (recent log) the error’s message is at this time is :

5178 2016-07-29 07:16:59 Client [UI Thread] VideoPlayer - ErrorEvent C:\Xibo Library\45.mp4. Ex = Le Lecteur Windows Media a rencontré un problème lors de la lecture du fichier.
After quite a lot of days of research, I made the proof which the problem turns around the proxy of this network, because players in local do not crash.
I verified the parameters proxy etc. and I found that it was also necessary to modify parameters proxy in the reader Windows media to player, or K-lite, VLC.
I am trying various scenarios, but at the moment, it does not still work.
I am in version 1.7.8 of Xibo.
Windows 7 pro for CMS and players.
Internet Explorer 11 and Windows Media to player 12.

Has anybody an experience of Proxy with Xibo?
Your notices and information would be welcome.
Thank you in advance.