See if your device has a GPX\Archive folder. That contains older archived trip logs that you can move to your PC (if you care to keep them) and delete. They will have a numbered name of 1.gpx, 2.gpx,...,20.gpx.
If you delete Temp.gpx and Current.gpx, that should remove any record of Waypoints. If you exported waypoints to your device under a different name, you may need to search for *.gpx to identify where on your device they were saved.
If you're on a Mac, empty the Trash before disconnecting.
Note: I'm only familiar with the Zumo line, so your Nuvi may be somewhat different. One of my Zumo devices hides some of the folders, so you may need to change Windows Explorer to display hidden files and definitely uncheck Hide known file types so you can see all file extensions.
The issue is, Basecamp has a issue using the "MTP" storage mode, change to "Mass Storage" and it will be ok. I beleive your Nuvi also uses the "MTP" mode as a default. Only the new Nuvis have the "MTP" mode. One thing you will need to do is press the computer "Safely remove Hareware" icon before you disconnect the USB cable. Your Nuvi will show up as a regular drive letter in the Explorer window and it will show as two drive letters when you use the "safely remove Hardware". This is normal and expected.
See my topic "cannont delete old route previously sent to Nuvi 2555LMT"
Never mind, found it, reposting here:
1. To make all of Nuvi files visible you must unhide protected files via Win7 like any other HD.
2. Start NUVI by itself and go to Volume Screen.
3. Press the upper right hand corner of screen for 10 seconds.
4. The Developers Screen will pop up
5. Scroll down to MTP SETTINGS
6. Change from AUTO DETECT to MASS STORAGE
7. Shut down NUVI and hookup to Computer USB cable
8. Start NUVI and it should recognize it is hooked up to the computer.
9. Explorer will now see all files in ROOT directory and the .System directories.