通过javascript使用回调发送图像到服务器

我试图通过回调方法在服务器上保存图像，当我尝试执行代码时，我得到异常演示代码示例:http://catalog.codeproject.com/Articles/17193/Upload-Images-Using-C-JavaScript-and-ASP-NET-2-0-C

流s = File.OpenRead(returnValue);在cs文件中，我遇到异常文件不存在

  <input id="File1" runat="server"  onchange="PopulateList(this)" name="File1" type="File" />
<script language="javascript" type="text/javascript">
    var counter = 1;
    var newPath = '';
    var filePath = '';

    function PopulateList(obj) {
        // Upload the image to the server folder 
        filePath = obj.value;
        // calls the server's method using client callbacks    
        CallServer(obj.value, '');
    }
    function ReceiveServerData(rValue) {
        // The new path will contain the path of the image which is inside the server's folder 
        newPath = rValue;
        alert(newPath);
        //CreateNestedElements();
    }
</script>

In Cs File

protected string returnValue = String.Empty;
protected void Page_Load(object sender, EventArgs e)
{
    string[] filePaths = null;
    //HtmlInputHidden hiddenControl = (HtmlInputHidden)Page.FindControl("list");
    //if (!String.IsNullOrEmpty(hiddenControl.Value))
    //{
    //    filePaths = hiddenControl.Value.Split('|');
    //    //SaveFilesToDB(filePaths);
    //}
    // register the callback script 
    string sbReference = ClientScript.GetCallbackEventReference(this, "arg", "ReceiveServerData", "context");
    string cbScript = String.Empty;
    // check if the script is already registered or not 
    if (!ClientScript.IsClientScriptBlockRegistered("CallServer"))
    {
        cbScript = @" function CallServer(arg,context) { " + sbReference + "}";
        ClientScript.RegisterClientScriptBlock(this.GetType(), "CallServer", cbScript, true);
    }
}

public string GetCallbackResult()
{
    string fileName = System.IO.Path.GetFileName(returnValue);
    string path = Server.MapPath("Images/");
    string fullPath = path + fileName;
    Stream s = File.OpenRead(returnValue);
    byte[] buffer = new byte[s.Length];
    s.Read(buffer, 0, (int)s.Length);
    int len = (int)s.Length;
    s.Dispose();
    s.Close();
    FileStream fs = new FileStream(fullPath, FileMode.Create);
    fs.Write(buffer, 0, len);
    Bitmap bmp = new Bitmap(fs);

    if (System.IO.Path.GetExtension(returnValue).Equals(".gif"))
    {
        bmp.Save(fs, ImageFormat.Gif);
    }
    else
    {
        bmp.Save(fs, ImageFormat.Jpeg);
    }
    bmp.Dispose();
    fs.Dispose();
    fs.Close();                      
    return "Images/" + fileName;
}
public void RaiseCallbackEvent(string eventArgument)
{
    if (!String.IsNullOrEmpty(eventArgument))
    {
        returnValue = eventArgument;
    }
}