登录成功以后用 UserManage.GetUserInfo().UserID获取登录用户的id会报错

protected void BtnLogin_Click(object sender, EventArgs e)
{
string userName = this.TxtUserName.Text;
string passWord = this.TxtPassWord.Text;

passWord = Utils.MD5(passWord, 16); //转为16位的md5加密

if (UserManage.CheckLogin(userName, passWord) == true)
{
CheckUserLogin.UpdateLoginInfo(userName, passWord, DateTime.Now, 0);
JS.Alert("恭喜，登录成功！"+UserManage.GetUserInfo().UserID);
}
else
{
JS.Alert("对不起登录失败！");
}
}