delphi中hook createprocess成功但无法成功卸掉钩子

我hook了CreateProcess，然而
启动我的程序并且启动钩子没有问题的，而且能成功挂上钩子。我运行一个程序的时候，会弹出提示信息“CreateProcess”。但是当我点Button2的时候，也就是说卸载了钩子的时候，却出现错误报告。大概是无法正常卸下钩子，引发错误报告的进程是资源管理器。请问是不是我的DLL中的代码中出现了什么问题？哪位大哥可以给我帮帮忙阿。谢谢dll所有代码如下///////
library MYAPIDLL;uses
  SysUtils,
  Windows,
  Classes,
  HookAPI in 'HookAPI.pas',
  Main in 'Main.pas';var
  Hook:HHOOK;function GetMsgProc(nCode:Integer;wParam:wParam;lParam:lParam):LRESULT;stdcall;
begin
  Result := 0;
end;procedure SetHook;
begin
  Hook := SetWindowsHookEx(WH_GETMESSAGE,GetMsgProc,hInstance,0);
end;procedure RemoveHook;
begin
  UnHookWindowsHookEx(Hook);
end;{$R *.RES}exports
  SetHook, RemoveHook;begin
  API_Hookup;
end.//////////////////////////////////////////////////////////////
unit Main;interface
uses
  SysUtils,
  Windows,
  ShellAPI,
  Dialogs,
  Classes;  procedure API_Hookup; stdcall;
  procedure API_HookDown; stdcall;type
   TCreateProcess = function(lpApplicationName: PChar; lpCommandLine: PChar;
      lpProcessAttributes, lpThreadAttributes: PSecurityAttributes;
      bInheritHandles: BOOL; dwCreationFlags: DWORD; lpEnvironment: Pointer;
      lpCurrentDirectory: PChar; const lpStartupInfo: TStartupInfo;
      var lpProcessInformation: TProcessInformation): BOOL; stdcall;
   TCreateProcessA = function(lpApplicationName: PAnsiChar; lpCommandLine: PAnsiChar;
      lpProcessAttributes, lpThreadAttributes: PSecurityAttributes;
      bInheritHandles: BOOL; dwCreationFlags: DWORD; lpEnvironment: Pointer;
      lpCurrentDirectory: PAnsiChar; const lpStartupInfo: TStartupInfo;
      var lpProcessInformation: TProcessInformation): BOOL; stdcall;
   TCreateProcessW = function(lpApplicationName: PWideChar; lpCommandLine: PWideChar;
      lpProcessAttributes, lpThreadAttributes: PSecurityAttributes;
      bInheritHandles: BOOL; dwCreationFlags: DWORD; lpEnvironment: Pointer;
      lpCurrentDirectory: PWideChar; const lpStartupInfo: TStartupInfo;
      var lpProcessInformation: TProcessInformation): BOOL; stdcall;var
   OldCreateProcess: TCreateProcess;
   OldCreateProcessA: TCreateProcessA;
   OldCreateProcessW: TCreateProcessW;implementationuses HookAPI;function MyCreateProcess(lpApplicationName: PChar; lpCommandLine: PChar;
      lpProcessAttributes, lpThreadAttributes: PSecurityAttributes;
      bInheritHandles: BOOL; dwCreationFlags: DWORD; lpEnvironment: Pointer;
      lpCurrentDirectory: PChar; const lpStartupInfo: TStartupInfo;
      var lpProcessInformation: TProcessInformation): BOOL; stdcall;
begin
   ShowMessage('MyCreateProcess');
end;function MyCreateProcessA(lpApplicationName: PAnsiChar; lpCommandLine: PAnsiChar;
      lpProcessAttributes, lpThreadAttributes: PSecurityAttributes;
      bInheritHandles: BOOL; dwCreationFlags: DWORD; lpEnvironment: Pointer;
      lpCurrentDirectory: PAnsiChar; const lpStartupInfo: TStartupInfo;
      var lpProcessInformation: TProcessInformation): BOOL; stdcall;
begin
   ShowMessage('MyCreateProcessA');
end;function MyCreateProcessW(lpApplicationName: PWideChar; lpCommandLine: PWideChar;
      lpProcessAttributes, lpThreadAttributes: PSecurityAttributes;
      bInheritHandles: BOOL; dwCreationFlags: DWORD; lpEnvironment: Pointer;
      lpCurrentDirectory: PWideChar; const lpStartupInfo: TStartupInfo;
      var lpProcessInformation: TProcessInformation): BOOL; stdcall;
begin
   ShowMessage('MyCreateProcessW');
end;procedure API_Hookup; stdcall;
begin
   if @OldCreateProcess = nil then
      @OldCreateProcess := LocateFunctionAddress(@CreateProcess);
   if @OldCreateProcessA = nil then
      @OldCreateProcessA := LocateFunctionAddress(@CreateProcessA);
   if @OldCreateProcessW = nil then
      @OldCreateProcessW := LocateFunctionAddress(@CreateProcessW);   RepointFunction(@OldCreateProcess, @MyCreateProcess);
   RepointFunction(@OldCreateProcessA, @MyCreateProcessA);
   RepointFunction(@OldCreateProcessW, @MyCreateProcessW);end;procedure API_HookDown; stdcall;
begin
   if @OldCreateProcess <> nil then
      RepointFunction(@MyCreateProcess, @OldCreateProcess);
   if @OldCreateProcess <> nil then
      RepointFunction(@MyCreateProcessA, @OldCreateProcessA);
   if @OldCreateProcess <> nil then
      RepointFunction(@MyCreateProcessW, @OldCreateProcessW);
end;end.finalization
  API_HookDown;
/////////////////////////////////////////////////////////////////
unit HookAPI;interfaceuses
   Windows, Classes;
function LocateFunctionAddress(Code: Pointer): Pointer;
function RepointFunction(OldFunc, NewFunc: Pointer): Integer;type //定义一个入口结构
   PImage_Import_Entry = ^Image_Import_Entry;
   Image_Import_Entry = record
      Characteristics: DWORD;
      TimeDateStamp: DWORD;
      MajorVersion: Word;
      MinorVersion: Word;
      Name: DWORD;
      LookupTable: DWORD;
   end;type //定义一个跳转的结构
   TImportCode = packed record
      JumpInstruction: Word; //定义跳转指令jmp
      AddressOfPointerToFunction: ^Pointer; //定义要跳转到的函数&#63729;
   end;
   PImportCode = ^TImportCode;
implementationfunction LocateFunctionAddress(Code: Pointer): Pointer;
var
   func: PImportCode;
begin
   Result := Code;
   if Code = nil then exit;
   try
      func := code;
      if (func.JumpInstruction = $25FF) then
      begin
         Result := func.AddressOfPointerToFunction^;
      end;
   except
      Result := nil;
   end;
end;function RepointFunction(OldFunc, NewFunc: Pointer): Integer;
var
   IsDone: TList;
   function RepointAddrInModule(hModule: THandle; OldFunc, NewFunc: Pointer): Integer;
   var
      Dos: PImageDosHeader;
      NT: PImageNTHeaders;
      ImportDesc: PImage_Import_Entry;
      RVA: DWORD;
      Func: ^Pointer;
      DLL: string;
      f: Pointer;
      written: DWORD;
   begin
      Result := 0;
      Dos := Pointer(hModule);
      if IsDone.IndexOf(Dos) >= 0 then exit;
      IsDone.Add(Dos);      OldFunc := LocateFunctionAddress(OldFunc);      if IsBadReadPtr(Dos, SizeOf(TImageDosHeader)) then exit;
      if Dos.e_magic <> IMAGE_DOS_SIGNATURE then exit;
      NT := Pointer(Integer(Dos) + dos._lfanew);      RVA := NT^.OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT]
         .VirtualAddress;      if RVA = 0 then exit;
      ImportDesc := pointer(integer(Dos) + RVA);
      while (ImportDesc^.Name <> 0) do
      begin
         DLL := PChar(Integer(Dos) + ImportDesc^.Name);
         RepointAddrInModule(GetModuleHandle(PChar(DLL)), OldFunc, NewFunc);
         Func := Pointer(Integer(DOS) + ImportDesc.LookupTable);
         while Func^ <> nil do
         begin
            f := LocateFunctionAddress(Func^);
            if f = OldFunc then
            begin
               WriteProcessMemory(GetCurrentProcess, Func, @NewFunc, 4, written);
               if Written > 0 then Inc(Result);
            end;
            Inc(Func);
         end;
         Inc(ImportDesc);
      end;
   end;begin
   IsDone := TList.Create;
   try
      Result := RepointAddrInModule(GetModuleHandle(nil), OldFunc, NewFunc);
   finally
      IsDone.Free;
   end;
end;end.