AVAbirami Varadharajan Syncfusion Team October 17, 2016 10:36 AM UTC
Thank you for contacting Syncfusion support.
The issue occurs due to the mismatch of ExcelVersion and file extension. To resolve the issue, we request you to set the workbook version as ExcelVersion.Excel97to2003 for “.xls” extension. Kindly use the below code sample.
workbook.Version = ExcelVersion.Excel97to2003;
If you are still facing the error, then kindly share us the issue reproducing sample which will be helpful for us to provide a prompt solution at the earliest.