2 issues with Facebook Sharing in Window Phone

Hello folks, I use TakeScreenShot() function (it's in the InteractiveConsole example in FB SDK for Unity) to take a screenshot and post it to FB. But there are 2 problems appeared:

• First: the screenshot that's captured is a gray blank like this: http://i7.minus.com/iXiHlCcSWaVfC.jpg

• Second: No one can see my post except me although I set the photo to public.

How can I fix these problems ? Thank you.

Here is the code of TakeScreenShot() function

 private IEnumerator TakeScreenshot() {
        yield return new WaitForEndOfFrame();
  
        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(new Rect(0, 0, width, height), 0, 0);
        tex.Apply();
        byte[] screenshot = tex.EncodeToPNG();
  
        var wwwForm = new WWWForm();
        wwwForm.AddBinaryData("image", screenshot, "InteractiveConsole.png");
        wwwForm.AddField("message", "herp derp.  I did a thing!  Did I do this right?");
  
        FB.API("me/photos", Facebook.HttpMethod.POST, Callback, wwwForm);
        Debug.Log("done");
 }