I think it's better to go from the bottom up when deleting rows

Also not sure why you wanted InStr

Not tested but maybe something like this

[vba]
nlastrow = Range("A65536").End(xlUp).Row


For nloop = nlastrow to 2 Step -1

If Cells(nloop,1).Value = Cells(nloop-1,1).Value Then
Rows(nloop).Delete
End If

Next nloop
[/vba]