Moving the rhino file sees obj texture get lost but why?

Hi,
V5.
purchase an object from sketchfab, had an obj.
imported the obj, into a new Rhino file, then set texture to object not layer, browsed to the jpg, then setObjectDisplayMode and rendered, and behold my object.

2 weeks later I move the .3dm file to a folder aptly named for what it is, should have made a folder initially but didnt.
open the .3dm , and see a silvery grey object, the texture has gone walkies.

why should moving the .3dm file break the link to the .jpg of the obj. which is still where I first saved the obj to.

and despite re-browsing to the jpg it now fails.

so thats now a problem, and why ?

Cheers

Steve