Smart Previews for ON the Road Files on NAS

I currently use LRC on macbook with all of my images stored on a NAS.  I normally build 1:1 previews and also have the "build smart previews" checked off.  Now I'm on the road with my NAS back home and on the left window of LRC it shows the folder containing the images as "missing" with the question marks which is normal.  I see the image placeholders but do not appear to have smart previews.

Any idea what I'm doing wrong or have set incorrectly?

thanks

tim