Sort Macro not working in 2003 (but ok in 2007)

Can anyone explain why this macro is working fine in 2007 and not in excel 2003:

Range("A1:C200").Select
    Range("C200").Activate
    ActiveWorkbook.Worksheets("#Client List").Sort.SortFields.Clear
    ActiveWorkbook.Worksheets("#Client List").Sort.SortFields.Add Key:=Range( _
        "A1:A200"), SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:= _
        xlSortNormal
    With ActiveWorkbook.Worksheets("#Client List").Sort
        .SetRange Range("A1:C200")
        .Header = xlGuess
        .MatchCase = False
        .Orientation = xlTopToBottom
        .SortMethod = xlPinYin
        .Apply
    End With
    Range("D1").Select

thanks