Screenshot script not uploading PNG to server when used with key trigger

Hello. I have tried using the script provided in the Unity documentation for uploading the screenshot to the server. It seems to work and upload the PNG to the server. I modified the script to run on a "Jump" button trigger. But it does not seem to work. The "Jump" button is not used by any other script. Here is the script #pragma strict

 function UploadPNG() { 
  
 // We should only read the screen after all rendering is complete 
 yield WaitForEndOfFrame();
 
 // Create a texture the size of the screen, RGB24 format
 var width = Screen.width;
 var height = Screen.height;
 var tex = new Texture2D( width, height, TextureFormat.RGB24, false );
 // Read screen contents into the texture
 tex.ReadPixels( Rect(0, 0, width, height), 0, 0 );
 tex.Apply();
  
 // Encode texture into PNG
 var bytes = tex.EncodeToPNG();
 Destroy( tex );
  
 // Create a Web Form
 var form = new WWWForm();
 form.AddField("frameCount", Time.frameCount.ToString());
 form.AddBinaryData("file", bytes, "screenShot.png", "image/png");
  
 // Upload to a cgi script
 var w = WWW("www.mydomain-s.com/unity/screenshot4/screenshot4.php", form);
 yield w;
 if (w.error != null){
 print(w.error);
 Application.ExternalCall( "debug", w.error);
 //print(screenShotURL);
 }
 else{
 print("Finished Uploading Screenshot");
 //print(screenShotURL);
 Application.ExternalCall( "debug", "Finished Uploading Screenshot");
 }
   
 } 
 
     
 function Update () {
 
         if(Input.GetButtonUp("Jump")){
             UploadPNG();
         }
     }
 

And here is the php script

     <?php
     if ((($_FILES["file"]["type"] == "image/png") || ($_FILES["file"]["type"] == "image/jpeg") || ($_FILES["file"]["type"] == "image/pjpeg")) && ($_FILES["file"]["size"] < 20000000000)) { if ($_FILES["file"]["error"] > 0) { echo "Return Code: " . $_FILES["file"]["error"] . "
     "; } else { echo "Upload: " . $_FILES["file"]["name"] . "
     "; echo "Type: " . $_FILES["file"]["type"] . "
     "; echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb
     "; echo "Temp file: " . $_FILES["file"]["tmp_name"] . "
     ";
      
     if (file_exists("upload/" . $_FILES["file"]["name"]))
     {
     echo $_FILES["file"]["name"] . " already exists. ";
     }
     else
     {
     move_uploaded_file($_FILES["file"]["tmp_name"], "upload/" . $_FILES["file"]["name"]);
     echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
     }
     }
     } else { echo "Invalid file"; }
     ?>

The web directory "Upload" has the write permissions set.

I'm stuck at it since hours. Would really appreciate the help.