Unable to authorize Plex server on PR2100

I recently had to replace a failing drive on my PR2100. The drive failed after I upgraded to OS5 but I don’t think that was the reason for the failure. I had been running RAID 0 so I had to rebuild the NAS. After I installed the Plex server, I clicked on the configure button. After logging in to Plex I get the big triangle with an exclamation point in the middle and a message that says Not authorized - you do not have access to this server. I never had a problem like this before and I have no idea what I need to do to resolve this issue. Can anybody help?

Same exact problem here, but on an EX2 Ultra. Upgraded to OS5, installed the latest version of PMS, and logged in using my credentials. It seemed to work fine, but I couldn’t add any new libraries. Then, when I closed the window and reopened the link, I got the “Not Authorized” error.

I’ve fully uninstalled and reinstalled PMS a few times now, both from the web interface and by downloading the BIN files manually from plex.tv. Guessing this is a Plex problem, not a WD one.