Не работает дозапись WriteFile - VB

Option Explicit
 
Private Const GENERIC_READ = &H80000000
Private Const GENERIC_WRITE = &H40000000
Private Const FILE_SHARE_READ = &H1
Private Const FILE_SHARE_WRITE = &H2
Private Const OPEN_EXISTING = 3
Private Const FILE_BEGIN = 0
Private Const INVALID_HANDLE_VALUE = -1
Private Const CREATE_ALWAYS = 2
Private Const OPEN_ALWAYS = 4
 
Private Type OVERLAPPED
  Internal As Long
  InternalHigh As Long
  offset As Long
  OffsetHigh As Long
  hEvent As Long
End Type
 
Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, lpSecurityAttributes As Any, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
Private Declare Function SetFilePointer Lib "kernel32" (ByVal hFile As Long, ByVal lDistanceToMove As Long, lpDistanceToMoveHigh As Long, ByVal dwMoveMethod As Long) As Long
Private Declare Function SetEndOfFile Lib "kernel32" (ByVal hFile As Long) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
Private Declare Function WriteFile Lib "kernel32" (ByVal hFile As Long, lpBuffer As Any, ByVal nNumberOfBytesToWrite As Long, lpNumberOfBytesWritten As Long, lpOverlapped As OVERLAPPED) As Long
 
Private Sub Command1_Click()
 
  Dim szPath As String
  Dim dwWrittenBytes As Long
  Dim OV As OVERLAPPED
  Dim hFile As Long
  Dim a() As Byte
 
  a = StrConv("privet", vbFromUnicode)
  szPath = "c:\myfile.txt"
  hFile = CreateFile(szPath, GENERIC_READ Or GENERIC_WRITE, FILE_SHARE_READ Or FILE_SHARE_WRITE, ByVal 0&, OPEN_ALWAYS, 0, 0)
 
  If hFile <> INVALID_HANDLE_VALUE Then
    Call SetFilePointer(hFile, 2, 0, FILE_BEGIN)
    Call WriteFile(hFile, a(0), UBound(a) + 1, dwWrittenBytes, OV)
    Call SetEndOfFile(hFile)
    Call CloseHandle(hFile)
  End If
 
End Sub