Private Sub UserForm_Activate()
Dim LRow&
Dim b_m1 As Boolean
Dim counterA%, counterB%

Erase a_allPos(): Erase a_allSec()

LRow = Sheets("ADM").Cells(Rows.Count, 1).End(xlUp).Row

counterA = 8: txt1 = "Раздел: "
counterB = 0: txt2 = "Делитель"
                    txt3 = Sheets("ADM").Cells(counterA, 1)
For counterA = 8 To LRow
                    txt4 = Sheets("ADM").Cells(counterA, 2)
                 If txt4 = "S" Then counterB = counterB + 1 'Маркер присутствует
                                    counterA = counterA + 1
Next

ReDim a_allPos(0 To counterB - 1, LRow + 1) 'Здесь не видит третий раздел после перезагрузки формы
      a_allPos(0, 0) = txt1 & txt3
ReDim a_allSec(counterB - 1)

counterA = 8
counterB = 0
counterC = 0: b_m1 = True

Do Until counterA = LRow + 1
              txt3 = Sheets("ADM").Cells(counterA, 1)
              txt4 = Sheets("ADM").Cells(counterA, 2)
          counterA = counterA + 1
   Select Case txt4
          Case "S"
          counterC = 0
          If b_m1 = False Then
          counterB = counterB + 1
             End If
             b_m1 = False
 a_allPos(counterB, 0) = txt1 & txt3 ' ошибку выдает в этой строке когда counterB=2
 a_allSec(counterB) = txt3
          Case "P"
          counterC = counterC + 1
 a_allPos(counterB, counterC) = txt3
          Case "!"
          counterC = counterC + 1
 a_allPos(counterB, counterC) = txt2
   End Select
Loop

---------Добавляю так------------------------------
Rows(counterC).Insert: Rows(counterC).RowHeight = 15

Sheets("ADM").Cells(counterC, 2) = "P"
Call ShowF_Create_Macro

Sub ShowF_Create_Macro() 'макрос на перезагрузку формы
Unload F_Create
       F_Create.Show
End Sub