Plex cant play films

I have a Ubuntu 16.04 Server with plex version 1.0.0.2261-a17e99e
When i try to play any film player says server unable to play it.
On 0.9.16.6.1993-5089475 version all fine
my /etc/fstab dont have any kind of plex records.
(Sry for my bad english)