Macro won't work twice

I have the following macro that I use to convert numbers stored as text to text. For some reason, if I try to use it twice in a row, it won't work, I get an error that says "application-defined or object-defined error" and highlights this part of the code:

Cells.SpecialCells(xlCellTypeLastCell) _
.Offset(1, 1).Copy

Sub ConvertToNumbers()
  Cells.SpecialCells(xlCellTypeLastCell) _
    .Offset(1, 1).Copy
  Selection.PasteSpecial Paste:=xlPasteValues, _
     Operation:=xlPasteSpecialOperationAdd
  With Selection
     .VerticalAlignment = xlTop
     .WrapText = False
  End With
  Selection.EntireColumn.AutoFit
End Sub