[Excel] Runtime Error 1004 in very simple script

[EmilN]

Hi I'm getting a Runtime Error 1004 @ the bolded line in the following script and I cannot understand why:

Public Sub MACRO()
    Dim x As Integer
    Dim y As Integer
    Dim n As Integer
    Sheets("Cognos").Select
    For x = 46 To 53
        For y = 13 To 639
            CellValue = Cells(y, x).Text
            Cells(y, x).Select
            If CellValue = "ADD SKU" Then
                Cells(y, 2).Resize(1, 1).Select
                n = ActiveCell.Value
                Sheets("Detail").Select
                NextRow = Cells(Rows.Count, 1).End(xlUp).Row + 1
                Cells(NextRow, 5).Select
                ActiveCell.Value = n               
                Sheets("Cognos").Select
            End If
        Next y
    Next x
End Sub

Any help would be greatly appreciated.