Here is a list of problems that may be the cause of problem :
1) Kml Path – Double check the path of file and make sure the file exists.
2) Missing mime types – You need to check for “KML” or “KMZ” mime type, if they are defined there on your server, if they are not then add
.kml application/vnd.google-earth.kml+xml .kmz application/vnd.google-earth.kmz
3) If none of above – The KML can’t be accessed since it’s on your local machine and google can’t access that since it doesn’t know how to get to localhost:8080
Hope it helps someone !