There is a file with bad data on your device. If you don't want to wait, you can rename the /Garmin/GPX folder on the device before starting BaseCamp. BaseCamp should start fine then. You can manually read the files from your renamed folder with File->Import.
This issue was fixed several months ago with 4.0.4. If you are already running BaseCamp 4.1.0, then the issue is probably a different issue. You can either revert to 4.0.4 or wait till next week for the fix to be released. Sorry for the inconvenience.