Files stored on a samba drive can't be opened. Neither can't files be saved to connected samba shares as they won't be shown in the save dialog.
The open/save dialogs are Windows standard dialogs. Did you perhaps create a mapping for these drives as another user than the one you're running N++ as? See:
I have a similar problem on Windows 7 Pro with n++ 6.6.8, as a local user (not a domain account) used windows explorer to map a network drive using a different account. Mapped drives show in windows explorer and command prompt yet does not show in n++ file dialogs. This is a change in behaviour as a few versions ago (I can't remember which) this worked fine. Any thoughts on how to work around this?