Route not Downloading to Satnav

[peter smith 3]

i have planned routes for an upcoming trip with 12 separate days all export successfully to my XT1 Garmin as Ive done previously except for one route. Im using a USB between Nav and laptop and never had this problem before, i have broken the route down but still no success. when i diconnect satnav and turn it on to look at a route it usually displays New Routes found but this is not happening so No Route
any ideas Peter