at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.Contexts.XlsxWorkbookImportContext.PairSeriesGroupsWithAxes()
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.Chart.PlotAreaElement.CopyPropertiesTo(IOpenXmlImportContext context, DocumentChart chart)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.Chart.ChartElement.CopyPropertiesTo(IOpenXmlImportContext context, DocumentChart chart)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.Chart.ChartSpaceElement.OnAfterRead(IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Elements.OpenXmlElementBase.Read(IOpenXmlReader reader, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Parts.ChartPart.Import(IOpenXmlReader reader, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.Model.Parts.OpenXmlPartBase.Import(Stream stream, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.OpenXmlImporter`1.ImportPartFromArchive(ZipArchiveEntry zipEntry, PartBase part, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.FormatProviders.OpenXml.OpenXmlImporter`1.Import(Stream input, IOpenXmlImportContext context)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.XlsxFormatProvider.ImportOverride(Stream input, CancellationToken cancellationToken)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.WorkbookFormatProviderBase.Import(Stream input, Nullable`1 timeout)

namespace Telerik.Windows.Documents.Model.Drawing.Charts
{
    /// <summary>
    /// Specifies where a chart legend is placed relative to the plot area.
    /// </summary>
    public enum LegendPosition
    {
        /// <summary>
        /// Positions the legend to the right of the plot area.
        /// </summary>
        Right,

        /// <summary>
        /// Positions the legend below the plot area.
        /// </summary>
        Bottom,

        /// <summary>
        /// Positions the legend to the left of the plot area.
        /// </summary>
        Left,

        /// <summary>
        /// Positions the legend above the plot area.
        /// </summary>
        Top
    }
}

WorksheetPageSetup pageSetup = workbook.ActiveWorksheet.WorksheetPageSetup;
pageSetup.PrintTitles.RepeatedRows = null;
pageSetup.PrintTitles.RepeatedColumns = null;

   at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
   at System.Collections.Generic.Dictionary`2.ContainsKey(TKey key)
   at Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.Model.Elements.Worksheets.ConditionalFormattingRuleElementX14.OnAfterRead(IXlsxWorksheetImportContext context) in C:\Work\document-processing\Documents\Spreadsheet\FormatProviders\OpenXml\Xlsx\Model\Elements\Worksheets\ConditionalFormatting\x14\ConditionalFormattingRuleElementX14.cs:line 62

            string inputFileName = "input.xlsx";
            if (!File.Exists(inputFileName))
            {
                throw new FileNotFoundException(String.Format("File {0} was not found!", inputFileName));
            }

            Telerik.Windows.Documents.Spreadsheet.Model.Workbook workbook;
            IWorkbookFormatProvider formatProvider = new Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.XlsxFormatProvider();

            using (Stream input = new FileStream(inputFileName, FileMode.Open))
            { 
                workbook = formatProvider.Import(input, TimeSpan.MaxValue);
            }
            string outputFilePath = "output.xlsx";

            using (Stream output = new FileStream(outputFilePath, FileMode.Create))
            {
                formatProvider.Export(workbook, output, TimeSpan.MaxValue);
            }
            Process.Start(new ProcessStartInfo() { FileName = outputFilePath, UseShellExecute = true });