Your problem is this
By default, Excel in Microsoft Windows uses the 1900 date system. However, many Apple Macintosh users use the 1904 date system.
Dates in Excel are actually numbers. That is, if you enter 1 in an empty cell and format the cell as date, 1900-01-01 is displayed
in the 1900 date system, and 1904-01-02 is displayed in the 1904 date system.
To change this setting in Excel 97-Excel 2003, on the Tools menu, click Options, and then click the Calculation tab. To change the
setting in Excel 2007, click the Microsoft Office Button, click the Excel Options dialog box, and then click the Advanced tab. If
you copy dates between workbooks, and both workbooks use a different date system, there is a difference of four years (1462 days)
between the dates.
The following steps illustrate one way to compensate for this difference:
Type 1462 into any empty cell in the workbook.
Copy the contents by selecting the cell and pressing CTRL+C.
Select the cell that contains the date you want to update.
Excel 2007 only:
On the Home tab, in the Clipboard group, click Paste, click Paste Special, select Add (or Subtract depending on which workbook you
are pasting to), and then click OK.
-or-
Excel 97, Excel 2000, Excel 2002, and Excel 2003 only:
On the Edit menu, click Paste Special, click Add (or Subtract depending on which workbook you are pasting to), and then click OK.
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Regards Ron de Bruin
http://www.rondebruin.nl/tips.htm