How to wait for unity webplayer to load and then invoke its function?

SO i tried this by making a call from unity awake/Start function to html javascript

``

 Application.ExternalCall( "SayHello", "The game says hello!" ); //void Start
 //on html side
 <script type="text/javascript" language="javascript">
 function SayHello( arg )
 {
 // show the message
 alert( arg );
 }

but this externall call never is made for some reason. My browser console says "'UnityObject2' is undefined" eventhough it is defined in html's js and the call from js to unity works fine

when i dont wait and find a way for it to be ready and invoke unity funtion like this

  u.getUnity().SendMessage("MyObject", "getCheckpoints", checkpointStringJSON);

it does not send the message firs time but does perfectly the second time. So i am guessing that unity is not loaded the first tie the function is being called.

thanking you in advance