Unfortunately, KML files are not really supported by GPSLog Labs (or the GPSBabel program we rely on to handle the many formats we do accept.)
You can use http://www.gpsvisualizer.com/ to convert your KML file to a GPX and then upload that or better still, use an app that saves your data in GPX format, which is the standard for transferring between devices and applications.
If you're good with Python, Ruby or Perl, you may be able to write a script to convert your KML file to a simpler CSV which will be supported by GPSLog Labs.