AsyncFileUpload issue on remote server

Question

On local server - everything is working fine (upload + JS alert).
On remote server - nothing is hapening, i think it is not firing.

This is the code:
<ajaxToolkit:AsyncFileUpload ID="AsyncFileUpload_picture" runat="server" OnClientUploadStarted="showUploadStartUpdateProgress" OnUploadedComplete="AsyncFileUploadUploadedComplete"
                                                            OnClientUploadComplete="showUploadEndUpdateProgress" OnClientUploadError="showUploadEndUpdateProgress"
                                                            Width="200" />
protected void AsyncFileUploadUploadedComplete(object sender, AsyncFileUploadEventArgs e)
        {
            var asyncFileUpload = (AsyncFileUpload)sender;
            string columnName = Convert.ToString(asyncFileUpload.ClientID);

            if (asyncFileUpload.HasFile)
            {
                //upload file here

                ScriptManager.RegisterStartupScript(this.Page, GetType(), "showAlert",
                   string.Format("alert('file uploaded');"), true); //alert after upload
            }
        }

Please advise
Thanks