You may have imported a track or created one in Basecamp software and this it has over the 25,000 maximum track points that will work in a New Generation Garmin GPS unit (GPSMap66/67 Series, Montana 7** Series)
(Please note Older GPS devices such as the etrex 20,22,30,32 series, eTrex Touch Series, Oregon Series, GPSMap62,64,65 & Montana 600 series will only work with a maximum number of 10,000 Track points)
If this is the case you can 'filter' them to the number you are wanting. To do this -
NOTE: When you filter track points, the removed points are permanently deleted from the track and the shape and distance of your track will change depending on how many points you reduce it by.
1. Right click on the track (when it is in the bottom left pane in Garmin BaseCamp)
2. Select - Filter selected track
3. Select an option: Select a point. ...
4. Select 'Entire track' under Filter.
5. Maximum points - change to 25,000 (10,000 if an older device)
6. Click OK