Cancel()

private Account myAccount;
Order stopOrder = null;
protected override void OnStateChange()
{
    if (State == State.SetDefaults)
    {
        // Initialize myAccount
    }
}
private void OnExecutionUpdate(object sender, ExecutionEventArgs e)
{
    // Cancel the stop order if an execution results in a long position
    if(e.MarketPosition == MarketPosition.Long)
        myAccount.Cancel(new[] { stopOrder });
}