New Post: [NPOI.XSSF.UserModel] XLSX file : repair needed when using Double in SetCellValue()

I faced the same problem and narrowed it down a bit.

On my German system with German culture info (i.e. comma as decimal separator), the XML files will be corrupt, regardless of the data type I am trying to write. Diff-ing the worksheet files revealed that this has to do with the basic sheet info being written at the end of the worksheets XML. The code generated on a German machine will be

<pageMargins left="0,7" right="0,7" top="0,75" bottom="0,75" header="0,3" footer="0,3"></pageMargins></worksheet> 

instead of

<pageMargins left="0.7" right="0.7" top="0.75" bottom="0.75" header="0.3" footer="0.3"></pageMargins></worksheet> 

Obviously this will throw an error with OpenOffice or Excel.

So I will use a forced US culture info for writing the data streams. This should take care of all file stream issues.