My GPSMAP 60CSx had started to become unreliable: crashing after startup, randomly locking up in mid route, and just generally being an aggravating piece of kit. I was really close to replacing it.
The problem seemed to appear after I’d used USB Mass Storage to transfer archived track logs to the computer. As a last resort, I tried removing the hidden files that OS X creates on every removable disk, and now all is well. It’s annoying and inexcusable that Apple chooses to do this, but we work around.
To delete these files from the terminal and eject the device safely, enter these commands:
pushd /Volumes/GARMIN/ rm -rf .Spotlight-V100 .Trashes ._.Trashes .fseventsd popd disktool -e disk1
Your device might not be called /Volumes/GARMIN/, so check and change appropriately. If you have multiple drives on your machine, your GPS is probably not the disk1 device. You can find out which it is by entering disktool -l.