PMS Update Cannot Be Installed

Hi I have tried to install PMS update Plex Media Server 1.12.3.4973 my Qnap TS 239 Pro, TS 453Pro and TS470Pro but on each get the message that the update cannot be installed. My Qnaps are currently running version 1.12.1.4885. I have also tried version 1.12.2.4929 but get same problem.
Qnaps TS453 Pro and TS470Pro are running firmware 4.3.4.0551 Qnap TS239 Pro running with firmware 4.2.6
This is the first time I have encountered such a problem. As I only use PMS for music library and not movies is there any need to update. If so I would appreciate suggestions. Thank you.