Can anyone tell me what's wrong with this code ??

Code:
        Dim input As IO.StreamReader = New IO.StreamReader(Application.StartupPath & "\dcm.rtf")
        Dim output As IO.StreamWriter = New IO.StreamWriter(Application.StartupPath & "\dcm\" & denumire_folder_destinatie & "\" & denumire_fisier_destinatie)
        Dim buffer As String = input.ReadToEnd

        buffer = buffer.Replace("[filiala]", Me.txt_filiala.Text)
        buffer = buffer.Replace("[data]", Me.txt_data_cm.Text)
        buffer = buffer.Replace("[seriacm]", Me.txt_seria_cm.Text)
        buffer = buffer.Replace("[numarcm]", Me.txt_nr_cm.Text)
        buffer = buffer.Replace("[numeprenume]", Me.txt_nume_prenume.Text)
        buffer = buffer.Replace("[cnp]", Me.txt_cnp.Text)
        buffer = buffer.Replace("[scoalaabsolvita]", Me.txt_scoala_absolvita.Text)
        buffer = buffer.Replace("[serienrds1]", Me.txt_serie_nr_ds1.Text)
        buffer = buffer.Replace("[serienrds2]", Me.txt_serie_nr_ds2.Text)
        buffer = buffer.Replace("[serienrds3]", Me.txt_serie_nr_ds3.Text)

        output.Write(buffer)
        input.Close()
        output.Close()
Is not replacing the stings and if i try tu change the strings for example "[filiala]" with "01filiala" etc... it's not replacing all of them!

Why ? What's wrong ?