Even if I delete unnecessary code and add number of paragraph, it still working the same: It is doing what I want to do with document but still with error: object variable or with block variable not set

Sub add_sign_xml()


Dim oPar As Paragraph


    For Each oPar In ActiveDocument.Range.Paragraphs
    If oPar.Range.Characters.First = "<" _  
    And Not InStrRev(oPar.Range.Text, "-") > 0 _
    And Not InStr(oPar.Next(1).Range.Text, "<tr>") > 0 Then 'I've added no. of paragraph
            oPar.Range.InsertAfter "add"
    End If
  
Next

End Sub