Many Garmin devices have a limit of how many points a gpx track might have. You can bypass the limit by splitting a GPS track to segments of 500 points or less. Here is how to do it with a free Qmapshack program:

As an example, I took a 100km ride track from Strawberry Fields Forever ride. (Click on the link, click on 100km, export tab, download as GPX)

Let’s see the complete track on map: In Qmapshack, File-> Load GIS Data, select the gpx file. “Open SFF 100K” folder in Data window and double-click on the track.

Lovely how Qmapshack shows map and terrain, isn’t it?

Let’s unlock the file, so it can be modified: right click on track, select edit, in the edit track tab that appears click on the lock icon and agree to unlock the file.

Now let’s split it: switch back to map view tab, click on a point on the track and select scissors on the menu that appears.

Note that new track name will show how many points it will contain. (unfortunately, I could not find any indication on how many points I am cutting off before I actually do it). Cancel if there are too many points, save if you like it. Save second portion. Agree to delete the original track.

Now repeat the operation until all you have are sub-500px tracks. If you place them into a single project, you can right-click and save the project folder as a single gpx file that contains multiple tracks – the file can be uploaded at once.

One important note – all the track segments must have names that differ in the first several characters, as Garmin devices limit the name lengths, and it might happen that, as you upload gpx tracks, the tracks will overwrite each other. Don’t worry, you can still go back to your project, unlock each segment and rename it by clicking its name by the lock icon.

Once on the device, select a color for all the track segments and check “show on map”.