Silverlight 运行时说缺少对象，代码如下,求

Silverlight 运行时说缺少对象，代码如下,求高手指点
<UserControl x:Class="SilverlightApplication1.MainPage"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
  mc:Ignorable="d"
  d:DesignHeight="350" d:DesignWidth="500">

  <Grid x:Name="LayoutRoot" Background="White">
  <Ellipse x:Name="MyElipse" Fill="White" Stroke="Black" Height="85" Margin="51,31,59,0" VerticalAlignment="Top" MouseEnter="myElipse_MouseEnter" MouseLeave="myElipse_MouseLeave"/>
  <Slider x:Name="MySlider" Height="5" Margin="41,246,47,0" VerticalAlignment="Top" Maximum="200" Minimum="10" Value="0" ValueChanged="MySlider_ValueChanged"/>
  </Grid>
</UserControl>


using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SilverlightApplication1
{
  public partial class MainPage : UserControl
  {
  public MainPage()
  {
  InitializeComponent();
  MySlider.ValueChanged += new RoutedPropertyChangedEventHandler<double>(MySlider_ValueChanged);
  }
  void MySlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
  {
  MyElipse.Width = MySlider.Value;
  MyElipse.Height = MySlider.Value;
  }

  private void myElipse_MouseEnter(object sender, System.Windows.Input.MouseEventArgs e)
  {
  // TODO: Add event handler implementation here.
  MyElipse.Fill = new SolidColorBrush(Colors.Blue);
  }

  private void myElipse_MouseLeave(object sender, System.Windows.Input.MouseEventArgs e)
  {
  // TODO: Add event handler implementation here.
  MyElipse.Fill = new SolidColorBrush(Colors.Red);
  }
  }
}


[解决办法]
这样很难判断问题在哪里。能把错误信息贴上来看看么？
[解决办法]

C# code

void MySlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)        {            if (MyElipse != null)            {                MyElipse.Width = MySlider.Value;                MyElipse.Height = MySlider.Value;            }        }
[解决办法]
你的应用初始化时就失败了，将MainPage中的 MySlider.ValueChanged += new RoutedPropertyChangedEventHandler<double>(MySlider_ValueChanged);
注释掉，然后看看是否有错误？如果没有错误，说明 MySlider.ValueChanged += new RoutedPropertyChangedEventHandler<double>(MySlider_ValueChanged);
有问题。
[解决办法]
我感觉是你的环境问题，你试着重新建一个SL工程 什么也不写 看看能不能运行