fileupload postedfile is null when getting from jquery to codebehind.

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ASP.NET

jQuery

Hi Iam yogesh sharma iam having problems in saving the postedfile from HTML input file
into some folder...
I Have to get the PostedFile of html input file using jquery and save that file into some folder from codebehind using webmethod. my problem is that when i checked the
file in webmethod by debugging i get the postedfile as NULL. I am getting the size of that file which is OK.But postedfile is null..
My Jquery Code Is.....

function SubmitImage_Click() {
                   var postedfile = ($("#fupdImg"))[0].files[0];
                   //alert(postedfile);
                   var exist = $("#fupdImg").val().split('.').pop();
                   PageMethods.GetNewImageName(exist, postedfile);                     
And My Code behind is....
<pre lang="c#">
[System.Web.Services.WebMethod()]
    [System.Web.Script.Services.ScriptMethod()]
    public static void GetNewImageName(string extension,HtmlInputFile file)
    {
        clsMNC obj = new clsMNC();
        string ssql = "select Count(ProductId)+1 from Product";
        Int32 pid = Convert.ToInt32(obj.getOneValue(ssql));
        string imgName = "img" + "_" + pid +"."+ extension;
        //return imgName;
        string savepath = HttpContext.Current.Server.MapPath(".") + "\\UserImgs\\";
        savepath += imgName;
        hp=file.PostedFile;

Here I want to save file.postedfile using SaveAs Method...
Please help, I am Trying Since 2 days but not getting answer from google..
Any Help wiil be appreciated...