Too many via points to load route on Zumo 665

There's a limitation on the number of via points in a route, not sure about the Zumo but AFAIK it's 200 on the nuvi. Your safest bet is to create the route separately and thus reduce the vias, or share the track with others.

b) on the Mac version of BaseCamp there is a setting under PREFERENCES:ROUTING entitled "Via Points Created When Converting A Track To A Route" On my system the default value is 50. See if the Windows version has such a setting.

a) That could be dues to the map you are using, e.g., it might not have any routable roads in that area or the Mapping datum perhaps.

Instead of converting the track to a route in BaseCamp, just put the track directly on the zumo. The 660 (and the 665 as it is almost the same) is capable of handling tracks (actually it converts a track to a route itself, but the algorithm that the zumo uses is better suited for this device than that of BaseCamp)

I have been using Garmin for years. My latest is the BMW Navigator IV that is the same as the Zumo 660. I have tried and failed over the years on countless occassions to successfully create a route in a timely fashion with Basecamp (on Mac).

I find Basecamp hopeless. I would agree, it is much easier to create a route on the Device itself. A trick I use is to find the points and click "Go" on the device. This saves them in "Recently found folder." I then go to Custom routes and create a new route in no particular order using all the new points. (Make sure your start and end points are correct though). You can add up to 200 points. I then go to Edit Route and rename it to what it should be and click on Optimally reorder points. Done! This is great for Route Optimisation for Business too! It would take me ages to do it on Basecamp even if Basecamp did not freeze all the time. Go the GPS!