'КЛАСС VB_PictureBox
Option Explicit
Public WithEvents Ctrl As VB.PictureBox
Public Index As Long

Private Sub Ctrl_Click()
  MsgBox "hwnd=" & Ctrl.hWnd
End Sub
 

Option Explicit
Private Sub Form_Load()
         Dim VB_PictureBox1 As New VB_PictureBox
         Set VB_PictureBox1.Ctrl = Form1.Controls.Add("VB.PictureBox", "pic1")
         Set VB_PictureBox1.Ctrl.Tag = VB_PictureBox1   '<---- ошибка
           
End Sub

VB_PictureBox1.Ctrl.Tag = ObjPtr(VB_PictureBox1)   

Dim VB_PictureBox2 As VB_PictureBox
CopyMemory VB_PictureBox2, CLng(VB_PictureBox1.Ctrl.Tag), 4

   Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" ( _
       lpvDest As Any, lpvSource As Any, ByVal cbCopy As Long)
   ' To Store An Object to a Long:
   Public Function Store(objThis As Object) As Long
      Dim iU As IShellFolderEx_TLB.IUnknown
      Set iU = objThis
      iU.AddRef
      Set iU = Nothing
      Store = ObjPtr(objThis)
      ' objThis cannot terminate until we call iU.Release on it
   End Function

   ' To Retrieve the Object From the Long Value:
   Public Function ObjectFromPtr(ByVal lPtr As Long) As Object
   Dim objT As Object
       ' Bruce McKinney's code for getting an Object from the
       ' object pointer:
       CopyMemory objT, lPtr, 4
       Set ObjectFromPtr = objT
       CopyMemory objT, 0&, 4
   End Function

   ' To Delete The Object:
   Public Function Delete(ByVal lPtr As Long) As Long
      Dim objThis As Object
      Set objThis = ObjectFromPtr(lPtr)
      Dim iU As IShellFolderEx_TLB.IUnknown
      Set iU = objThis
      iU.Release
      Set iU = Nothing
      Set objThis = Nothing
      ' objThis now terminates if there are no other external
      ' references to it.
   End Function

        Set VB_PictureBox1.Ctrl.Tag = VB_PictureBox1   '<---- ошибка

Option Explicit

Private Sub Form_Load()

  Dim VB_PictureBox1 As VB.PictureBox
  Set VB_PictureBox1 = Form1.Controls.Add("VB.PictureBox", "pic1")
  
  '---------------------------------
  Dim Var1 As Variant
  Set Var1 = VB_PictureBox1
  '---------------------------------
 
  Dim VB_PictureBox2 As VB.PictureBox
  Set VB_PictureBox2 = Var1
  MsgBox VB_PictureBox2.Name
End Sub