I've been struggling with a NullReferenceException and hope someone here will be able to point me in the right direction. I'm trying to create and populate a DataTable and then show the results in a DataGridView control. The basic code follows, and Execution stops with a NullReferenceException at the point where I invoke the new UpdateResults_Delegate. Oddly enough, I can trace entries.Rows.Count successfully before I return it from QueryEventEntries, so I can at least show 1) entries is not a null reference, and 2) the DataTable contains rows of data. I know I have to be doing something wrong, but I just don't know what.

private delegate void UpdateResults_Delegate(DataTable entries);

private void UpdateResults(DataTable entries)
{
    dataGridView.DataSource = entries;
}

private void button_Click(object sender, EventArgs e)
{
    Thread t = new Thread(new ThreadStart(PerformQuery));
    t.Start();
}

private void PerformQuery()
{
    DateTime start = new DateTime(dateTimePicker1.Value.Year,
                                  dateTimePicker1.Value.Month,
                                  dateTimePicker1.Value.Day,
                                  0, 0, 0);

    DateTime stop  = new DateTime(dateTimePicker2.Value.Year,
                                  dateTimePicker2.Value.Month,
                                  dateTimePicker2.Value.Day,
                                  0, 0, 0);

    DataTable entries = QueryEventEntries(start, stop);
    Invoke(new UpdateResults_Delegate(UpdateResults), entries);
}

private DataTable QueryEventEntries(DateTime start, DateTime stop)
{
    DataTable entries = new DataTable();
    entries.Columns.Add("colEventType", typeof(Int32));
    entries.Columns.Add("colTimestamp", typeof(Int32));
    entries.Columns.Add("colDetails",   typeof(String));

    ...
    conn.Open();
    using (SqlDataReader r = cmd.ExecuteReader())
    {
        while (r.Read())
        {
            entries.Rows.Add(result.GetInt32(0),
                             result.GetInt32(1),
                             result.GetString(2));
        }
    }
    return entries;
}