I use a NFS (network file system protocol) file server with SketchUp 2016 on MacOS Sierra with no problem.
SketchUp 2017 reports “File not found or invalid” when trying to open any file. “Save As” onto the server works fine.
SMB/CIFS file servers work fine too (with both 2016/2017).
FIXED:
The reason for the problem was mandatory file locking when opening .skp files introduced with SU 2017.
If you have an NFS server that doesn’t support locking, use option ‘locallocks’ (not ‘nolockd’) when mounting the file system on MacOS.