UPdating XML, getting "Object Reference Not Set To An Instance Of An Object"
<p>I am trying to update 3 pieces of data in an XML document but getting an "Object Reference Not Set To An Instance Of An Object" error.  This is the XML file format I am trying to update:</p>

<pre><code>&lt;?xml version="1.0" encoding="US-ASCII" standalone="true"?&gt;
&lt;ExportSettings xmlns="CompanyName" ExportName="Data Export" Dataset="TestName"&gt;
  &lt;General&gt;
     &lt;AsOfDate&gt;03/31/15&lt;/AsOfDate&gt;
     &lt;PriceDate&gt;03/31/16&lt;/PriceDate&gt;  
  &lt;/General&gt;
  &lt;Source&gt;
      &lt;Set&gt;Set Name&lt;/Set&gt;
  &lt;/Source&gt;
&lt;/ExportSettings&gt;
</code></pre>

<p>This is the C# code that is throwing the error:</p>

<pre><code>    private void btnUpdate_Click(object sender, EventArgs e)
    {
        try
        {
            {
                string strAsOfDate = dateTimePickerAsOfDate.Text;
                string strPriceDate = dateTimePickerPriceDate.Text;
                string strSetName = txtboxSet.Text;

                XmlDocument doc = new XmlDocument();
                doc.Load(strXMLfilepath);
                XmlNode General;
                XmlNode root = doc.DocumentElement;
                General = root.SelectSingleNode("/ExportSettings/General");
                General["AsOfDate"].InnerText = strAsOfDate;
                General["PriceDate"].InnerText = strPriceDate;
                XmlNode Source;
                Source = root.SelectSingleNode("/ExportSettings/Source");
                Source["Set"].InnerText = strSetName;
                doc.Save(strXMLfilepath);

            }
        }
        catch (System.Exception excep)
        {
            MessageBox.Show(excep.Message);
        }
    }
</code></pre>

<p>Can anyone see the problem?  I am not very familiar with updating XML so there may be something basic wrong here.</p>