TwoCheckout System.ArgumentNullException : Value cannot be null Parameter name: s
<p>I'm trying to integrate my code with 2checkout payment SDK available here:
<a href="https://github.com/2Checkout/2checkout-dotnet" rel="nofollow">https://github.com/2Checkout/2checkout-dotnet</a></p>

<p>This below code throws the following error:</p>

<blockquote>
  <p>System.ArgumentNullException : Value cannot be null. Parameter name: s</p>
</blockquote>

<pre><code>[Test]
public void _004_TestSaleStop()
{

    TwoCheckoutConfig.ApiUsername = "username";
    TwoCheckoutConfig.ApiPassword = "password";
    TwoCheckoutConfig.Sandbox = true;


    try
    {

        var ServiceObject = new SaleService();
        var ArgsObject = new SaleStopServiceOptions();
        ArgsObject.sale_id = 9093729066354;
        var result = ServiceObject.Stop(ArgsObject);
        Assert.IsInstanceOf&lt;TwoCheckoutResponse&gt;(result);
    }
    catch (TwoCheckoutException e)
    {
        Assert.IsInstanceOf&lt;TwoCheckoutException&gt;(e);
    }
}
</code></pre>

<p>The error is internal to their code, so it's hard to know why this is thrown.</p>

<p>I've seen some articles suggest that the ASP.NET process does not have write permission. So I right-clicked the solution and added "IIS_IUSRS" with all perms. This doesn't help either.</p>

<p>Any help would be greatly appreciated.</p>