Error mount_denied

The server refused to share that folder

The MOUNT request failed with an error other than access denied or not found — the path is a file, is too long, or the server hit an internal error.

What this means

The MOUNT service on the server answered with an unusual status. The alert names it: not a folder, name too long, not supported, or a server fault.

Check

• Is the path a folder? An export path that points at a file returns not a folder. Use Find Shared Folders to pick from what the server actually exports.
• Very long paths — over 255 characters per component — are refused.
• Server fault means the server’s mountd hit an internal error: a disk that isn’t mounted, a dataset that’s locked (encrypted TrueNAS datasets after a reboot), or a corrupt exports table. Check the NAS’s storage page and its NFS log.
• Not supported from MOUNT is rare and usually means a minimal userspace server. Try NFS Version → NFSv4 (no MOUNT protocol at all).