Hi Jaeyeol Shin,
Thank you for using Syncfusion products.
Inorder to reproduce the above reported NullReferenceException we need an excel file which reproduces the issue while opening with XlsIO.Silverlight.Could you please get back to us with the excel file which reproduces the issue so that we are able to proceed further on this.
In Addition to the above reported exception one of our engineer is addressed the issue with the following solution. We have given below the same for your reference.
The reported error occurs as the excel engine is not disposed after the workbook operations are completed. Please close / dispose the workbook and Engine once the operations are completed as shown below:
workbook.Close();
excelEngine.Dispose();
And also the reported issue may occur because the usage of multiple instances of workbook and excel engine in an application. Please use the single instance of an workbook and an excel engine that will
not reproduce the issue where the XlsIO follows the same.
Please try the above solution at your side and let us know if these helps you.
Please let me know if you require any further clarifications.
Thanks,
Sridhar.S