I generated the attached Excel file by opening an existing file, populating a datasheet, and then saving and closing the file. When I use another API to open the file, it errors out with "Invalid shared string item". If I open the file in Excel and then close it, Excel prompts me to save it. Once I save it, it opens fine. Can you tell what's wrong with the file that causes Excel to think it needs to be saved, even if nothing has changed?