Html 5 formdata file upload issue with asp.net webservice

I'm having an strange issue with html5 formdata. i'm using the html5 form data to send a file to the server via jquery ajax request. then using asp.net webservice to receive the posted file and saving the file to a directory.

This process worked fine locally. once i published to the server I'm getting an internal server error 500.

once I ran the website locally inside the sever its working. I think the issue with web server cant access the client path?

  var formData = new FormData();

  for (var i = 0; i < uploadFileArray.length; i++) {

        var f = uploadFileArray[i];   
            formData.append('file' + i, f.file);
    }

    formData.append('indexdate', indexDate);
    formData.append('status', status);
    formData.append('category', category);
    formData.append('comments', comments ? comments : '');

    $.ajax({
        type: "POST",
        url: serviceUrl,
        data: formData,
        cache: false,
        contentType: false,
        processData: false,
        beforeSend: function () { $defer.notify(); },
        success: function (response) {

            $defer.resolve(response)
        },
        error: function (jqXHR, textStatus, errorThrown) {

            $defer.reject(textStatus);

        }
    });

Web Service

      <WebMethod(EnableSession:=True)> _
Public Function UploadFiles() As String

    Try
         Dim postedContext As HttpContext = HttpContext.Current            

        Dim indexDate As String = postedContext.Request.Form("indexdate")

        Dim status As Integer = Convert.ToInt32(postedContext.Request.Form("status"))

        Dim docCategoryKey As String = postedContext.Request.Form("category")

        Dim comments As String = postedContext.Request.Form("comments")

        ' Get the file collection 

        Dim request As HttpFileCollection = postedContext.Request.Files

        For Each filename As String In request

            Dim file As HttpPostedFile = request(filename)

            'Validate the data

            If file Is Nothing Then
                Throw New System.IO.FileNotFoundException("Please upload a valid file")
            End If

            SaveFiles(file, docCategoryKey, comments, status, indexDate)

        Next
    Catch ex As Exception
        Throw ex
    End Try
    Return ""
End Function