Media Folder Not Found

[ajnabi1957]

Hi, Brand new to Subsonic. I'm trying to set up my media folders which is stored on an external drive. The path is correct but there is a red letter message saying, Folder Not Found.
I use an iMac with OS10.12.6 (sierra)
I use iTunes at the moment but will soon be using Swinsian as my library.
My library is 585G, stored on external drive WD4Tb
Subsonic details as follows: Version 6.1.1 (build 2a8e8d) – May 31, 2017
Server jetty-6.1.x, java 1.8.0_92, HSQLDB, Mac OS X (48.2 MB / 123.5 MB)
Appreciate any advice.

PS. Once I have Subsonic set up and working I want to listen through Sonos Playbase and Play1.
Sonos plays fine from my iPhone and desktop, do no issues with Sonos
Thank you!
Look forward to your wisdom and advice.
Nate