Running Macros based on Worksheet changes in Excel 2007

Hello,

I ran into a problem with a macro created in Excel 2002 that runs when the values of certain cells in the worksheet changes using

Private Sub Worksheet_Change(ByVal Target As Range)

However, when I tested this in Excel 2007, it doesn't initiate the macro. Whats causing it to not work in 2007 even though it works in 2002?

Thanks.