Are you creating / adding the chart from the scratch. For example, if you are creating and instantiating a new workbook by using, e.g Workbook wb = new Workbook(), here you may specify the file formatting type to XLSX and save the file to XLSX file format instead of XLS. See the line of code that you may use instead:
Workbook wb = new Workbook(FileFormatType.Xlsx);
For your information IV is the last column for an XLS file format (MS Excel 97 - 2003), so the chart is created based on the data range within the range Ax:IVx. So, you can always save the file in XLSX file format which does not have IV column’s limitation.
Let us know if you still have any problem or confusion.