Can someone troubleshoot this code for me please?

Private Sub Worksheet_Change(ByVal Target As Range)
If Intersect(Target, Range("B1,B2")) Is Nothing Then
   Exit Sub
 Else
      If Intersect(Target, Range("B1")) Then
        Application.EnableEvents = False
        Range("B2").Formula = "=(B1 * 2)"
        Application.EnableEvents = True
   ElseIf Intersect(Target, Range("B2")) Then
        Application.EnableEvents = False
        Range("B1").Formula = "=(B2 / 2)"
        Application.EnableEvents = True

  End If
  End If
End Sub
It works when I input into B1, but gives me an error on input of B2.