Code Hangs when Authorizing in SharpBox for Windows Phone 8 with C#

Question

I want to create an WP8 app that allow user to upload images to their dropbox account. Just one click of the button it will authorize if haven't already then upload the image, otherwise it just uploads it.

I followed the instructions here to create the following codes for the event-handler:

private async void toDropBoxBtn_Tap(object sender,System.Windows.Input.GestureEventArgs e)
{
        DropBoxConfiguration config = CloudStorage.GetCloudConfigurationEasy(nSupportedCloudConfigurations.DropBox) as DropBoxConfiguration;
        DropBoxRequestToken requestToken = DropBoxStorageProviderTools.GetDropBoxRequestToken(config, "MY KEY", "MY SECRET"); // The code hangs at this line
        String AuthorizationUrl = DropBoxStorageProviderTools.GetDropBoxAuthorizationUrl(config, requestToken);
        ICloudStorageAccessToken accessToken = DropBoxStorageProviderTools.ExchangeDropBoxRequestTokenIntoAccessToken(config, "7nu03leznnz6x74", "ex3gge8av7kp9lq", requestToken);
}

The code just hangs at the 2nd line with no error or exception. I don't know what I've do wrong. Feel free to ask for more information. Thank you.