winform中Log4Net使用笔记

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="log4net"
             type="log4net.Config.Log4NetConfigurationSectionHandler,log4net"/>
  </configSections>
  <log4net>
    <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
      <param name="File" value="Log\Log.txt" />
      <param name="AppendToFile" value="true" />
      <param name="MaxSizeRollBackups" value="100" />
      <param name="MaximumFileSize" value="2MB" />
      <param name="RollingStyle" value="Size" />
      <param name="StaticLogFileName" value="true" />
      <layout type="log4net.Layout.PatternLayout">
        <param name="ConversionPattern" value="%-5p %d [%c] %m%n" />
      </layout>
    </appender>
    <root>
      <level value="all" />
      <appender-ref ref="RollingLogFileAppender" />
    </root>
  </log4net>
</configuration>

System.Configuration.ConfigurationErrorsException: 配置系统未能初始化 ---> System.Configuration.ConfigurationErrorsException: 每个配置文件中只允许存在一个 <configSections> 元素，并且，如果存在该元素，它还必须是根 <configuration> 元素的第一个子元素。

static class Program
    {
        static log4net.ILog LOG = log4net.LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main()
        {
            //捕获未处理异常
            Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException);
            Application.ThreadException += new System.Threading.ThreadExceptionEventHandler(Application_ThreadException);
            AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);

            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new FormMain());
        }
        static void Application_ThreadException(object sender, System.Threading.ThreadExceptionEventArgs e)
        {
            LOG.Error(e.Exception);
            //throw new Exception("线程未知异常", e.Exception);
            MessageBox.Show(e.Exception.Message, "线程异常", MessageBoxButtons.OK, MessageBoxIcon.Error);
            Application.Exit();
        }

        static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
        {
            Exception ex = e.ExceptionObject as Exception;
            LOG.Error(ex);
            MessageBox.Show(ex.Message, "应用程序异常", MessageBoxButtons.OK, MessageBoxIcon.Error);
            Application.Exit();
        }
    }