I have a similar issue. My DVR and STB are working normally but on the My Verizon site I get the same error which is "Your STB record cannot be found".
do i need to order the "home media dvr" service in order to use the multi-room dvr option? i have an HD dvr downstairs, but my sd stb upstairs cannot see it. there's an error message that says something like "There was a problem with your multiroom dvr..."
i've re-booted both the dvr, sd stb and the router.
i can use the web remote dvr to schedule recordings to the hd dvr, if this helps at all.