Could you be more precise, I think that I have updated permissions, it does not solve it...
(I can only update permission on Admin > file manage, on host, I do not have permission, but I think it is normal).

I use Host > Vendor (and not admin > vendor), does it change something John ???
I have restarted the application, does not work better...

:-(

DV

I was plenty of hope... I done this, on ALL folders, it does not solve the problem...

You had the problem on a fresh install John, and you solve it by refreshing rights on file manager ?? Am I alone with this problem, any idea is welcomed, it is very annoying for me, so I would like to get ride of it instead of going back to 4.4.1...

 DV

My ISP has reset my folders. He has also recurse permission. It does not help, still the problem.

See the answer of my host provider:

I've reset your folders now.  In fact, folders permission includes read/write/execute for Network Service.  
One thing though ... if it's working for one DNN user and not another, it's a DNN issue, not server/OS permissions.  From a server/OS/IIS perspective, all of the DNN users have the same permissions (that of Network Service).  DNN does, however, add another layer of security on top of that.  Don't know if that's the issue, but something worth considering. 

Any other idea ??
DV FX