Managed users cannot connect to the content server

I have set my sister up as a managed user and installed the Plex app on her Samsung Blue-Ray player at her house. When I select her (or others) from the list of managed users I can see the libraries but when I try to play any movie I get the error message ‘Unable to connect to the content server’. If I select myself from the user list I can play the movies without error. My son can play media remotely just fine from his house with a Roku as a managed user. I can play movies at home with the managed users and if I use my cellphone with wifi turned off to simulate a remote connection I can play movies fine from any managed user. The only thing that seems constant is the Plex app on her Samsung Blue-ray player but I can’t find anything in the settings of the app and it plays everything fine if she uses my user profile but or course this messes up who has watched what and how far through they are. I have uninstalled the Plex app from my sisters Samsung and reinstalled and re-authorised it through plex.tv but the problem remains. Can anyone help with this?

Phil Doomen