Hey again. Reread my post and hope it didn't come off as condescending, just trying to sort out vocabulary
Anyway seems like PC3 is set up correctly. So either there is some tweaking to your LAN to do or PC2 is not configured in the same way as PC3.
Couple of questions/confirms:
1- are you using authentication (not required but useful when you want to sync and do admin from client to server). If not, I'd use that (set in options on "PC1").
2- on your LAN have you assigned fixed IP addresses to each PC. Or through the DHCP setting in your router is your router assigning them? (IMO the latter is easiest). If not I'd recommend doing so.
3-"M:\\" is your mapped network drive? All three PCs see it in Win explorer - good. From the tree in JRiver -- go to Drives and Devices/Explorer ... do both PC2&3 see the M:\\ drive? Is it also visible under Network just below, same place?
4) In options on each client are they set like this (PC2&3 only)?
5) In options on the server (PC1 only), are they configed like this?
6) If 1-5 are ok, then you should see something like this on the client machines (PC2&3), depending on what zones you have set-up. No zones then there would just be just the default Player and There:Player
Note: I renamed the library "Downstairs" so it won't show up like that. If you are loading a local library on a client (eg: "Main" which is confusing as IMO it should say LOCAL default or something similar), add a new library and enter the authentication code (access key) from PC1's options.
and this on the server (PC1)
Now there are other ways to do this depending on your system and what you want to do, but I'd start by using authentification and DHCP IP control via the router. You can use fixed ip addresses without authentication or other options, but IMO this setup is easiest to debug if you have issues. Once it all works you can get fancy if you want
PS - Strongly recommend excluding network drives (your M) from your AV scans and make sure your firewall is not blocking LAN ports on the LAN or port 52199