I have this VBA excel macro code

```
Sub fillcells()
    Range("J14").Select
    Do While ActiveCell <> Range("J902")
        ActiveCell.Copy
        ActiveCell.Offset(6, 0).Select
        ActiveCell.PasteSpecial
    Loop
End Sub

```

At first it was working fine but now sometimes when I try to run the macro the loop suddenly stops at cell J242, other times is arising an error 'mismatch type' and sometimes the macro just select cell J14 without doing the loop