The Garmin Communicator Plugin must be installed for this to work with your Garmin.
Tracks are split into sections of < 500 waypoints. So for example, Adm McHardy Way will appear in the Tracks menu as 1_AdmMchardy and 2_AdmMcHardy.
Some older models may accept only 250 points per saved track, and will truncate the track. If this happens you can use software such as GPS TrackMaker to load the GPX track as an Active Log into the live memory of your Garmin, which doesn't have this limit.