Between the 2003 and the most recent versions, the number of rows that can be reached in an Excel sheet has changed significantly. As a result, the VBA codes prevent the portability of your workbook ...

To ensure that Excel converts your date to a number enter it like this, without quotes: "4/4/2011". Then click on cell "A2" and enter the later of the two dates in the same manner.

Click on the column header to select the location for your date information. In the Home tab on the Excel ribbon, click on the arrow at the bottom right corner of the Number section.