Hi bploh, maybe you should perform hard reset (clear all user data)?
Turn off Nuvi, then press and hold lower right corner of Nuvi screen, turn on Nuvi, continue to hold (the screen) until you get the prompt to clear all user data, select Yes. Important: Before performing hard reset, back up current.gpx from ..\Garmin\GPX folder. After successful reset, rename backed up current.gpx to temp.gpx and place it in ..\Garmin\GPX folder. Note: After resetting Nuvi, it's also advisable to let Nuvi gather satellite data outdoors and stationary, until GPS fix is obtained.
If after hard reset, still the same, I'd advise you back up all files and folders in Nuvi (including hidden files), and format it using PC (just like a USB drive), and then replace all files.
Thanks for your recommendation.
I tried to hard reset but couldn't work. I wanted to try the format it but didn't dare as I was worried that it would delete the system files as well. I know that this might solve the problem as the similar problem happened before on my USB drive.
I was playing around and manage to free up the space using this method.
In windows explorer, go to Folder Options > View. Uncheck "Hide protected operating system files".
Browse to Garmin drive (e.g. E:). I saw a "Recycled" folder in my Garmin. All deleted files were in the Recycled folder. I deleted all files in that folder hence free up the space