SiverLight to Javascript Communication : Failed to invoke exception

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Silverlight

This is Silverlight Code :

var selecteditem = objModel.Cells.Where(i => i.IsSelected == true).ToList();         
int[] cid = selecteditem.Select(o => o.CellId).ToArray();
string[] mac = selecteditem.Select(p => p.MACAddress).ToArray();
int mode = 0;
for (int i = 0; i < cid.Length; i++)
{
  nodeStream.Add(new NodeStreamJson
  {
    MACAddress = mac[i]
  });
}
DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(List<NodeStreamJson>));
MemoryStream ms = new MemoryStream();
ser.WriteObject(ms, nodeStream);
ms.Position = 0;
StreamReader sr = new StreamReader(ms);
string nObj = sr.ReadToEnd();
if (objModel.SelectedCell != null)
{
  System.Windows.Browser.HtmlPage.Window.Invoke("StartStream", nObj, mode);
}

Java Script Code:

function StartStream(nObj, mode)
{
var nodeObj = JSON.parse(nObj);
linkConditioningHubstart.server.multiplenodestreaming(nodeObj, mode);
}

This is my Silverlight code. I call SilverLight to Javascript Communication.
When i run first time it's working good. and stop the process(stop buton) and call again start button i got below error message

InvaildOperationException was unhandled by user code
Failed to Invoke : StartStream

StarkTrace
{System.InvalidOperationException: Failed to Invoke: StartStream.
at System.Windows.Browser.ScriptObject.Invoke(String name, Object[] args)
at ProView.Views.ToolsView.LcStart_Click(Object sender, RoutedEventArgs e)
at System.Windows.Controls.Primitives.ButtonBase.OnClick()
at System.Windows.Controls.Button.OnClick()
at Telerik.Windows.Controls.RadButton.OnClick()
at System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
at System.Windows.Controls.Control.OnMouseLeftButtonUp(Control ctrl, EventArgs e)
at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex,
Int32 actualArgsTypeIndex, String eventName, UInt32 flags)}

Pls Help Me