SaveFileDialog 提示尝试读取或写入受保护的内存。这通常指示其他内存已损坏

private void ExportExcel()

        {

            DataTable dtVilationList = Grab.GetVilationList(guid.ToString());



            SaveFileDialog dlg = new SaveFileDialog()

            {

                Filter = "*.xls|*.xls",

                RestoreDirectory = true,

                FileName = DateTime.Now.ToString("yyyyMMddhhmmss")

            };

            if (dlg.ShowDialog() == DialogResult.OK)

            {

                string[] columns = new string[] {

                    "车牌","违规时间","违规行为","违规地点","罚款金额","扣分","异地办理费"

                };

                int i = 0;

                foreach (string c in columns)

                {

                    dtVilationList.Columns[i++].ColumnName = c;

                }

                CSD.Tools.DownExcel downExcel = new CSD.Tools.DownExcel();

                downExcel.Width(0, 16);

                downExcel.Width(1, 18);

                downExcel.Width(2, 35);

                downExcel.Width(3, 35);

                downExcel.Width(6, 16);

                downExcel.File(dtVilationList, dlg.FileName);

                MessageBox.Show("导出成功！", "系统提示", MessageBoxButtons.OK, MessageBoxIcon.Information);

            }

        }

第一次SaveFileDialog 是正常显示，并能保存，，再次点击导出Excel的话会报错误,
错误定位在，“ if (dlg.ShowDialog() == DialogResult.OK)”
错误信息：尝试读取或写入受保护的内存。这通常指示其他内存已损坏。
数据是从Access读取的