Contents of my KML:
<?xml version="1.0" encoding="UTF-8"?> Plum_Canyon_Elementary.kml normal #s_ylw-pushpin highlight #s_ylw-pushpin_hl 1.1 http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png 1.3 http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png Plum_Canyon_Elementary 1 Take_OFF_WayPoint_1 -118.4858174358298 34.44723814425289 0 20.0571584380187 64.75913458194374 104.3230817041583 relativeToSeaFloor #m_ylw-pushpin 1 -118.4860465155611,34.44692526413344,0 Way_Point_1 -118.4849897072927 34.44677147169661 0 20.0576266430135 64.75925921823867 119.5786860889212 relativeToSeaFloor #m_ylw-pushpin 1 -118.4848228596487,34.44697885188158,0 Way_Point_3 -118.4837808969226 34.4463025411175 5.349952906528214 20.05823090110044 63.41892109697542 98.79412852014191 relativeToSeaFloor #m_ylw-pushpin 1 -118.4835775003268,34.44618160122284,0 Way_Point_4 -118.4834679487485 34.44809964196731 0 20.05831798638995 61.94408786346126 68.62186401704734 relativeToSeaFloor #m_ylw-pushpin 1 -118.4834666352848,34.4482152145771,0 Way_Point_5 -118.4849185882807 34.44858102084847 0 24.02020571237862 61.09705050202899 60.65131237747275 relativeToSeaFloor #m_ylw-pushpin 1 -118.4850638514953,34.44874661081251,0 Way_Point_6 -118.4861294431589 34.44824610721747 0 24.01952077803007 61.09706857129218 62.94912692870996 relativeToSeaFloor #m_ylw-pushpin 1 -118.4862358718267,34.4483292529208,0 Way_Point_7 -118.4864397101933 34.44755566836804 0 24.01934526218016 61.09747983291791 115.315837432379 relativeToSeaFloor #m_ylw-pushpin 1 -118.4867544478399,34.4473093692914,0 Way_Point_8 -118.486365038592 34.44763353618244 3.763207371231738 24.01938746867211 61.09785619954848 163.0938880427348 relativeToSeaFloor #m_ylw-pushpin 1 -118.486547301453,34.44699830224105,0What software was used to create a KML mission? What is displayed in your post is not valid KML but that is most likely due to tags being stripped.
Provide more details about how your KML file was generated. That may help to diagnose the problem.