Easy solution.
- Uninstall PMS (use the first radio button - Uninstall Only – KEEP – option)
- Reinstall PMS again — HOWEVER
- Select the “Install using Plex Claim Token” (2nd radio button) method
- Click “Get Plex Claim Token” hyperlink
- Browser will open and show you a claim token
- COPY the token
- Return to the installation tab and PASTE the token into the window on the form.
- Click NEXT NEXT DONE.
- It will update the credentials in the server using that token.
- If all is well, It will show your username (claimed by:) when it finishes.
- Now open normally