Since POI-1.8, I have not been able to use POI to open an existing XLS or XLT and add data. When I open the resulting document, all cells are blank. However, if I view the file in a Hex viewer, such as Textpad, I see the new data in the file. Therefore, the resulting document must be corrupt. I have example input, output, and code that I can forward, if interested.
Created attachment 7058 [details] Input XLS File (Just an empty workbook)
Created attachment 7059 [details] Code to open file and add data.
Created attachment 7060 [details] Resulting corrupted XLS
Please note that I have attached said input, output, and code.
This appears to be related (if not same) bug as reported by 14824. Marcin Nowak makes an interesting observation, which is, "There is simple workaround for this problem. Modify sheet in Excel putting (for example) one space into cell (0,0)." I tried this workaround with success. I suggest closing this bug in deference to 14824.
*** This bug has been marked as a duplicate of 14824 ***