Disk sharing error

Hi, I have installed nextcloud on ubuntu 16.10 and I have a problem when I try to share a mounted disk in /media/tagotis/Program this always appears to me with the red box and without access

Any suggestions Thank you.

Sorry for my english is translated from google.

I think it might be that the second one is a subdirectory of the first one. You can also use the admin-user from the first external storage and let him share the subfolder to a subgroup (via file-app).