VB.NET调用FORMATMESSAGE出现内存错误提示，求大神关照

Imports System.Runtime.InteropServices

Public Class Form1

<DllImport("Kernel32.dll", EntryPoint:="FormatMessageW", SetLastError:=True, CharSet:=CharSet.Unicode, CallingConvention:=CallingConvention.StdCall)>
Public Shared Function FormatMessage(ByVal dwFlags As Integer,
                                     ByRef lpSource As IntPtr,
                                     ByVal dwMessageId As Integer,
                                     ByVal dwLanguageId As Integer,
                                     ByRef lpBuffer As [String],
                                     ByVal nSize As Integer,
                                     ByRef Arguments As IntPtr) As Integer
End Function

Public Const FORMAT_MESSAGE_FROM_SYSTEM = &H1000
Public ErrorString = "12345678"

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

    Dim Bytes As Long
    Static aa As IntPtr

    Bytes = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, aa, Err.LastDllError, 0, ErrorString, 128, aa)
    lstResults.Items.Add(Bytes)
End Sub

End Class

帮下忙噻，据说还要十个字

会的人告诉一下呗 卡住这里好久了