I had a problem this morning I've seen before when trying to copy folders over a LAN from my Mac to NAS - (while using the PP software to mount the drive(s) on the desktop = pink icons) - 

Here's the error I got -

"The operation can’t be completed because an unexpected error occurred (error code -50)."

I was able to alternatively mount the drive via SMB ('cause it's a Dockstar) and transfer files just fine.