I have a samsung UN55C8000 manufactured in 2010 Plex App 1.019. I can access the PMS on my network with my master user id. If I try to use another user sign in using the code entered into their plex.tv/link I can sign in but can't reach the PMS. I'm able to login as another user on a newer Samsung TV.
Have the exact same issue, except mine is a "D" model (2011). Not sure why the SmartHub forum we're in is across such a broad range. Ours are almost "too old" and different than the later ones.
The old 1.0 version doesn't support user switching because it was not available on the server at time of release.
Unfortunately the new 2.0 version can only be used on 2012 and newer models.
The 1.0 version does however support shared servers if that's what you are looking at.
It just works a bit different and is called "Shared Content".
You can download the manual for here which explains how to set it up.