NullReferenceException on instantiating line calling new
<pre><code>static void Main()
{
    AppHelper helper = new AppHelper();
    // more stuff
}
</code></pre>

<p>The above compiles fine using csc.exe but throws NullReferenceException at runtime:
Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.
   at AppHelper..ctor()</p>

<pre><code>public class AppHelper
{
    private string connect = System.Configuration.ConfigurationManager.ConnectionStrings["connectionString"].ToString();

    public AppHelper()
    {
        // TODO
    }
}
</code></pre>

<p>Debugger locates connectionString from app.config but running the executable chokes.</p>
