Macro works fine in Excel 2003 but not in 2007

I have a spreadsheet designed to adjust golf handicaps for a small group of golfing friends and record the results in an archive. It worked fine in Excel 2003 but crashes on the second use in Excel 2007.
I have attached the spreadsheet. To see the problem go to Sheet "Scores" and click on Enter Sample Score, then "Update Handicap". The score and revised handicap will be recorded in the archive sheet.
Do the same thing again and the programme crashes with run-time error 1004. I can't see a problem?
I have looked at lots of forums and the best I can find is reference to Excel 2007 creating some "hidden variables" that don't clear properly but I can't understand it and can't see where my spreadsheet might do this.
Any help will be appreciated.