Jumplist in SilverLight

Hi,
I am doing a SilverLight application. In that app , i want to create a jump list.
I am able to create the jumplist but when i click on that its showing Invalid Parameter.
What can be the issue. I am new to using NESL features.
The code is as below.
private void CreateJumplist()
{
//create first item
JumpListItem Task1 = TaskbarButton.Current.Jumplist.CreateJumpListItem(1);
Task1.Title = "Task 1";
Task1.Description = "This is task 1";
Task1.CommandLineArguments = "Hello World";
Task1.Category = "My Tasks";
//create second item
JumpListItem Task2 = TaskbarButton.Current.Jumplist.CreateJumpListItem(2);
Task2.Title = "Task 2";
Task2.Description = "This is task 2";
Task2.CommandLineArguments = "This is NESL";
Task2.Category = "My Tasks";
//show minimized + inactive
Task2.ShowCmd = ShowWindowState.SW_SHOWMINNOACTIVE;

//create – order in collection determines order of display
TaskbarButton.Current.Jumplist.SetJumpListItems( new JumpListItem[] { Task1, Task2 });
return;
}
Any help appreciated. Thanks