[Problem] D3D9-Hook funzt nur manchmal

// dllmain.cpp : Defines the entry point for the DLL application.
#include "windows.h"
#include "stdafx.h"
#include <cstdio>
#include <time.h>
#include <d3d9.h>
#include <d3dx9.h>
#define _CRT_SECURE_NO_WARNINGS

void add_log(char* format, ...);
DWORD WINAPI HookThread(void);
void* DetourFunc(PBYTE src, const PBYTE dst, const int len);
DWORD dwFindPattern(DWORD dwAddress,DWORD dwLen,BYTE *bMask,char * szMask);
bool bDataCompare(const BYTE* pData, const BYTE* bMask, const char* szMask);

HRESULT __stdcall hkEndScene(LPDIRECT3DDEVICE9 pDevice);
typedef HRESULT(__stdcall* EndScene_t)(LPDIRECT3DDEVICE9);
EndScene_t pEndScene;

HANDLE tmpHandle = NULL;
HMODULE hModD3D9 = NULL;
FARPROC dwEndScene = NULL;
DWORD* VTableStart = NULL;
DWORD tempadd = NULL;
bool bMessageSent = false;
const D3DCOLOR txtGreen = D3DCOLOR_ARGB(255, 0, 255, 0);

BOOL APIENTRY DllMain( HMODULE hModule, DWORD  ul_reason_for_call, LPVOID lpReserved)
{
	switch (ul_reason_for_call)
	{
		case DLL_PROCESS_ATTACH:
			add_log("==========LOG START==========");
			add_log("DLL Attached");
			add_log("Creating Thread...");
			tmpHandle = CreateThread(0, 0, (LPTHREAD_START_ROUTINE)&HookThread, 0, 0, 0);
			if (!tmpHandle)
			{ 
				add_log("ThreadCreation Failed!");
			}
			break;
		case DLL_PROCESS_DETACH:
			add_log("DLL Detached");
			add_log("==========LOG END==========\n\n\n");
			break;
	}
	return TRUE;
}

DWORD WINAPI HookThread(void)
{ 
	add_log("Thread Created");
	while (!hModD3D9)
	{
		add_log("Searching d3d9.dll...");
		hModD3D9 = GetModuleHandle(L"d3d9.dll");
		Sleep(100);
	}
	add_log("Found d3d9.dll: %x !", hModD3D9);

	tempadd = dwFindPattern( (DWORD)hModD3D9, 0x128000, (PBYTE)"\xC7\x06\x00\x00\x00\x00\x89\x86\x00\x00\x00\x00\x89\x86", "xx????xx????xx");
	VTableStart = (DWORD*) *(DWORD*)(tempadd+2);
	dwEndScene = (FARPROC) VTableStart[42];
	add_log("Found EndScene: %x !", dwEndScene);
	pEndScene = (EndScene_t) DetourFunc((PBYTE) dwEndScene, (PBYTE)hkEndScene, 5);
	return 0;
}

HRESULT __stdcall hkEndScene(LPDIRECT3DDEVICE9 pDevice)
{
	if (bMessageSent == false)
	{
		add_log("Message from inner EndScene!");
		bMessageSent = true;
	}
	D3DRECT rect = {10, 10, 310, 310};
	pDevice->Clear(1, &rect, D3DCLEAR_TARGET, txtGreen, 0, 0);
	return pEndScene(pDevice);
}

void add_log(char* format, ...)
{ 
	HANDLE filehandle;
	DWORD dwReadBytes;
	char buffer[2048];
	char writebuffer[2048];
	va_list args;
	va_start(args, format);
	vsprintf (buffer, format, args);
	filehandle = CreateFile(L"Log.txt", GENERIC_WRITE, 0, 0, OPEN_ALWAYS, 0, 0);
	SetFilePointer(filehandle, 0, 0, FILE_END);
	char date[18];
	_strdate(date);
	date[8] = ' ';
	_strtime(date+9);
	sprintf_s(writebuffer, 2048, "Log Added (%s): %s\r\n", date, buffer);
	WriteFile(filehandle, writebuffer, strlen(writebuffer), &dwReadBytes, 0);
	CloseHandle(filehandle);
}

void* DetourFunc(PBYTE src, const PBYTE dst, const int len)
{
	DWORD dwback;
	BYTE* jmp = (BYTE*)malloc(len+5);
	VirtualProtect(src, len, PAGE_READWRITE, &dwback);
	memcpy(jmp, src, len);
	jmp += len;
	jmp[0] = 0xE9;
	*(DWORD*)(jmp+1) = (DWORD)(src + len - jmp) - 5;
	src[0] = 0xE9;
	*(DWORD*)(src+1) = (DWORD)(dst - src) - 5;
	VirtualProtect(src, len, dwback, &dwback);
	VirtualProtect(jmp-len, len+5, PAGE_EXECUTE_READWRITE, &dwback);
	return (jmp - len);
}

bool bDataCompare(const BYTE* pData, const BYTE* bMask, const char* szMask) 
{
	for(;*szMask;++szMask,++pData,++bMask)
	{
		if(*szMask=='x' && *pData!=*bMask )
		{
			return false;
		} 
	} 
	return (*szMask) == NULL;
}

DWORD dwFindPattern(DWORD dwAddress,DWORD dwLen,BYTE *bMask,char * szMask)
{
	for(DWORD i=0; i < dwLen; i++) 
	{
		if( bDataCompare( (BYTE*)( dwAddress+i ),bMask,szMask) )
		{
			return (DWORD)(dwAddress+i); 
		}
	}
	return 0; 
}

Log Added (01/30/12 01:21:06): ==========LOG START==========
Log Added (01/30/12 01:21:06): DLL Attached
Log Added (01/30/12 01:21:06): Creating Thread...
Log Added (01/30/12 01:21:06): Thread Created
Log Added (01/30/12 01:21:06): Searching d3d9.dll...
Log Added (01/30/12 01:21:06): Found d3d9.dll: 6b050000 !
Log Added (01/30/12 01:21:06): Found EndScene: 6b07279f !
//hier wäre es ohne der add_log Zeile in der gehookten Funktion zu Ende gewesen
Log Added (01/30/12 01:21:06): Message from inner EndScene!
//hier hatte ich dann das Programm geschlossen
Log Added (01/30/12 01:21:09): DLL Detached
Log Added (01/30/12 01:21:09): ==========LOG END==========

void* DetourFunc(PBYTE src, const PBYTE dst, const int len)
{
	DWORD dwback;
	BYTE* jmp = (BYTE*)malloc(len+5);
	VirtualProtect(jmp, len+5, PAGE_EXECUTE_READWRITE, &dwback);
	VirtualProtect(src, len, PAGE_READWRITE, &dwback);
	memcpy(jmp, src, len);
	jmp += len;
	jmp[0] = 0xE9;
	*(DWORD*)(jmp+1) = (DWORD)(src + len - jmp) - 5;
	src[0] = 0xE9;
	*(DWORD*)(src+1) = (DWORD)(dst - src) - 5;
	VirtualProtect(src, len, dwback, &dwback);
	return (jmp - len);
}

	if (bMessageSent == false)
	{
		add_log("Message from inner EndScene!");
		bMessageSent = true;
	}