Check if file exists and the required drives are connected

Server Version#: 1.24.5.5173-7000
Player Version#: any

Today I have migrated from a Synology DS218j to DS920+. When I wanted to see how much the performence of Plex had improved, I decided to play something from my tv. Unfortunately, I get the same error message for each video:

"Playback error

Check if the file exists and the required drives are connected"

On my phone I get the message that: “The media is not available. The connected file is not accessible for the server. Check if the file exists and if the required station is accessible.”

I suspect this has something to do with me migrating to a new NAS. Unfortunately, when I add another library, it does not see any of the files from the folder I select.

How do I solve this?

For each of the shared folders which contain your media:

Even though you had previously set permissions for “Plex”,

With DSM 7, you must now grant permission for "System Internal User’ PlexMediaServer to read the shares. ( Control Panel - Shared Folders )

We were forced to change username on DSM 7.

From system to system, the ID number for “PlexMediaServer” is subject to change (because it’s Linux underneath)