Using ToString() on int value in dynamic property assignment gives parsing internal error: "Value cannot be null. (Parameter 'left')"

[JanJorgensen]

This does not work:

    var value = System.Int64.Parse(text);
    while (true) : Stoppable
    {
        value++;
        secondaryToolBar.textbox.Text = value.ToString();
        delay(1ms);
    }