Range references not working

[j_Southern]

Can anyone explain why this piece of code doesn't work?

Sub FillDown()
 Dim a As Integer
 With Sheets("Orders_Sage")
     a = Me.TBRow.Value
    .Range(.Cells(a, 1)).Value = "Z"
     
    ' .Range("AD11").Offset(a - 10, 0).Value = Me.CBCylSize.Value
    End With

End Sub

I do get a value for a and I am trying to test to make sure the Cylsize value ends up in the right place.
I just get an error, whichever way I designate the range
John