Plex App shows error on KDL -32HX753

[JADASTIC]

Hi, So I have set up a Plex server on my PC. My TV '32HX753' is connected to the same network and so is my other TV 46W905A and so is another TV 24W605A. Running the PLEX app on all tv's the 32HX753 is the only one that doesn't find the server. I can see the PLEX media server within the Server Display Settings within Home Network setup. But the TV just shows an error. The PLEX app starts, then I get a message "do I want to launch Internet Browser?" I select "NO" and then my PLEX USER icon appears. I type in the 4 digit code and the error message shows. An Error occurred.  Make sure server is online and the requested media is supported. 

My video media is a mixture of MP4, AVI and Mkv file containers but PLEX has the capability to transcode the video file. So why does my 32" TV not work with the App. I must note that this TV is also the only one that doesn't work with anything other than MP4 when I use the standard DLNA, whereass the other TV's play the other formats with no problem.

Am I missing something, or will it just not work on this TV. There must be a setting I've missed. Any help or suggestions. Regards.