Makro stürzt ab

Private Sub Stichwortsuche_Click()
' Makro sucht Schlüsselwörter  
'  
 Dim y As Integer

If TextBox1.Value <> "" Then                                     
      Documents.Open FileName:=Textdokument, ReadOnly:=False    
              
    If Right(Textdokument, 5) = ".docx" Then       
       Windows(Textdokument).Activate           
          
        Dim oDoc As Document
        Set oDoc = ThisDocument
        
        Set rDoc = ThisDocument                                     
        a = rDoc.Tables(1).Rows.Count                               
        For i = 2 To a                                             
            b = Left(rDoc.Tables(1).Cell(i, 1).Range.Text, _
            Len(rDoc.Tables(1).Cell(i, 1).Range.Text) - 2)
            c = Left(rDoc.Tables(1).Cell(i, 2).Range.Text, _
            Len(rDoc.Tables(1).Cell(i, 2).Range.Text) - 2)
           
  
        Selection.HomeKey Unit:=wdStory
        Selection.Find.ClearFormatting
        With Selection.Find
            .Text = (b)                                 
            .Replacement.Text = ""  
            .Forward = True
            .Wrap = wdFindStop
            .Format = False
            .MatchCase = False
            .MatchWholeWord = True
            .MatchWildcards = False
            .MatchSoundsLike = False
            .MatchAllWordForms = False
        End With
      
        Do While Selection.Find.Execute
          Selection.Comments.Add Range:=Selection.Range, Text:=(c) 
   
          y = y + 1
        Loop
        Next
          
          
    Else:
        If Right(Textdokument, 4) = ".doc" Then                                 
           Windows(Textdokument & " [Kompatibilitätsmodus]").Activate  
            
            Set rDoc = ThisDocument
            a = rDoc.Tables(1).Rows.Count                             
            For i = 2 To a
                b = Left(rDoc.Tables(1).Cell(i, 1).Range.Text, _
                Len(rDoc.Tables(1).Cell(i, 1).Range.Text) - 2)          
                c = Left(rDoc.Tables(1).Cell(i, 2).Range.Text, _
                Len(rDoc.Tables(1).Cell(i, 2).Range.Text) - 2)         
           
            Selection.HomeKey Unit:=wdStory                
            Selection.Find.ClearFormatting
            With Selection.Find
                .Text = (b)                                         
                .Replacement.Text = ""  
                .Forward = True
                .Wrap = wdFindStop
                .Format = False
                .MatchCase = False
                .MatchWholeWord = True
                .MatchWildcards = False
                .MatchSoundsLike = False
                .MatchAllWordForms = False
            End With
      
            Do While Selection.Find.Execute
            Selection.Comments.Add Range:=Selection.Range, Text:=(c)        
             y = y + 1
            Loop
            Next
                       
                Else: MsgBox "Falsches Dateiformat"  
                      Windows(Textdokument).Close             
           End If 
      End If
   
Else:
     
End If
End Sub

Private Sub Textdokument_auswählen_Click()
' Textdatei wählen.  
 
    Dim fd As FileDialog

    Set fd = Application.FileDialog(msoFileDialogFilePicker)

    With fd
        .AllowMultiSelect = False
        If (VerzeichnisUnused) Then
            .InitialFileName = Textdokument.Path & "\"   
            VerzeichnisUnused = False
        End If
        
        If .Show = -1 Then
            Datei = True
                    
            Textdokument = .SelectedItems(1)
            TextBox1.Value = Textdokument

        Else
        End If
    End With
    Set fd = Nothing
End Sub