Downloading File: no lines are ever executed

I am attempting to download a xml file and write it locally in my Unity3D Game(Target platform PC/Mac).

My Problem: The code to download the file never executes. I am unsure whats going wrong? The Debug.Log() commands inside the function downloadFile() are never output for some reason?

Important info:

• The target platform is PC & Mac standalone

• I am running the game through the Unity editor

• I dont have Unity3D Pro - do I need it to run code/games that download files

• Will this code work on Android/iOS target platforms or do I have to use native code to download &/or write a file to the platform/OS?

Can you tell me whats wrong with my code?

 public static IEnumerator downloadFile(string url, string outFile)
 {
     Debug.Log ("Start 1");
     bool res = false;
     WWW www  = new WWW(url); 
     Debug.Log ("Start 2");
     
     // wait until the download is done
     while(!www.isDone) {
         Debug.Log(www.progress);  
         yield return www; 
     }
     
     Debug.Log ("Start 3");
     if (www.isDone) {
         System.IO.File.WriteAllBytes(outFile, www.bytes);
         Debug.Log ("SUCCESS");
     }
     else Debug.Log ("FAIL");
 }

 // This code is in the function OnGUI()
 if (GUI.Button (new Rect(620,0,100,20), "Download")) {
     Debug.Log ("PRESS 1");
     downloadFile("http://www.fileden.com/files/2011/10/6/3205286/HomePremium.zip",
                                          "Assets/_TEST_FILES/_GENERATED/downloaded.xml");
     Debug.Log ("PRESS 2");
 }