Application.ExternalCall Issue

Hey folks, I've just got started a project which is using a combination of the Unity WebPlayer and a js framework for the UI, but I'm facing a problem trying to make the WebPlayer call a js function in my web page. I know that the way to achieve it is to call the Application.ExternalCall function from Unity, but for some unknown reason it doesn't seems to work for me, while I have no problems calling a Unity function from the webpage calling the getUnity().SendMessage method.

Basically, what I'm trying to do is to get reference to all the lights in the scene, create a List of serializable classes with just some basic informations, serialize a JSON string from the list and finally pass the resulting json to the javascript function in my page. Here's the script attached to an empty game object in the scene:

 public class Environment : MonoBehaviour {
             
     void Start () {
         Light[] Lights = FindObjectsOfType(typeof(Light)) as Light[];
         List<LightModel> LightRecords = new List<LightModel>();
                 
         foreach (Light light in Lights) {
             LightModel record = new LightModel();
             record.name = light.name;
             record.intensity = light.light.intensity;
             
             LightRecords.Add(record);
         }
                 
         string json = JsonConvert.SerializeObject(LightRecords);
         Application.ExternalCall("loadStore", json);
         Debug.Log(json);
     }
         
 }

and this is the javascript function in my webpage:

 <script type="text/javascript" language="javascript">
     <!--
     function loadStore( arg )
     {
         // show the message
         alert( arg );
     }
     -->
 </script>
     

For some reason, the alert is never shown..

You can notice a Debug.log at the end of the Unity Script. Trying to run the scene from unity the json is logged correctly so everything works there

 [{"name":"myLight","intensity":1.0},{"name":"dayLight","intensity":0.5}]

Can you guys shed some light here on what I'm doing wrong? Any help will be highly appreciated!

Thanks