Files produced by Excel 2007 are in the new .xlsx format. No other version of Excel can read them unless a special compatibility pack has been installed.

If you plan to share your Excel 2007 files with other Excel users, you can set Excel 2007 to save your files automatically in Excel 97-2003 format. This will allow other Excel users who have not upgraded to Excel 2007 to read your files.

How to set Excel 2007 to automatically save files in Excel 97-2003 format:

1. Start up Excel 2007. Open an empty worksheet.

2. Click the Office button at top left (the one with the four color Windows 2003 logo). This brings up a menu with: New – Open – Convert - Save – Save As etc.

3. At the bottom of the window, click onto the “Excel Options” button. There’s a list of options to the left, headed “Popular”.

4. Click onto the fourth one down – Save. To the right of Save it says: "Save files in this format." In the box it says "Excel Workbook (*.xlsx)."

5. Click on the down arrow at the right of the box. A list appears.

6. Click on the fourth item – "Excel 97-2003 Workbook (*.xls)."

7. Click OK at the bottom of the window.

To check that your change has worked:

You should now be back in the blank Excel worksheet. Click on the colored Office button again. This time select: Save As. The Save As box appears. At the bottom it should say: Save as type Excel 97-2003 workbook.

Thank you to David Carter and our sister site, accountingweb.co.uk for this tip.