I have checked this thoroughly and it looks like you need to use the new format with these files inside with the new folder convention:
1. /xl/workbook.xml
2. /xl/worksheets/sheet1.xml
3. /xl/theme/theme1.xml
4. /xl/styles.xml
5. /xl/sharedStrings.xml
6. /docProps/core.xml
7. /docProps/app.xml
I substituted the sheet1.xml the program created worksheet.xml and modified the sharedStrings.xml and it works.
I noticed for the worksheet - you used inlineStr format so I created an empty sharedStrings.xml file:
<?xml version="1.0" encoding="UTF-8" standalone="true"?>
<sst uniqueCount="0" count="0" xmlns="
http://schemas.openxmlformats.org/spreadsheetml/2006/main"/>