Here is the exact code I have tried. I also noticed that it will not export as an xml extension, it exports as xls even though I have the file name specified.
private void radBtnExcel_Click(object sender, EventArgs e)
{
ExportData();
}
void ExportData()
{
//ExportToExcelML exporter = new ExportToExcelML(radGv);
var excelML = new ExportToExcelML(radGv);
excelML.ExportVisualSettings = true;
radGv.Columns["Success Ratio"].ExcelExportType = DisplayFormatType.Custom;
radGv.Columns["Success Ratio"].ExcelExportFormatString = "0:#0.000%; (0000#);none";
excelML.SheetMaxRows = ExcelMaxRows._1048576;
excelML.RunExport("c:\\#support\\CTCStatistics.xml");
}