Problem with CLR / It don't work with Runtime v4.0.30319

I have a C++ dll which is calling my C# code after an injection with CLR.

So this is my C++ (dll) code:

#include "stdafx.h"
#include <iostream>
#include <metahost.h>
#include <atlbase.h>
#include <atlcom.h>
#pragma comment(lib, "mscoree.lib")

#define IfFailRet(expr)                { hr = (expr); if(FAILED(hr)) return (hr); }
#define IfNullFail(expr)                { if (!expr) return (E_FAIL); }

extern "C" int __declspec(dllexport) CALLBACK CallClrMethod(
    const WCHAR *AssemblyName,
    const WCHAR *TypeName,
    const WCHAR *MethodName,
    const WCHAR *args,
    LPDWORD pdwResult
)
{
    int hr = S_OK;
    CComPtr<ICLRMetaHost> spHost;
    hr = CLRCreateInstance(CLSID_CLRMetaHost, IID_PPV_ARGS(&spHost));
    CComPtr<ICLRRuntimeInfo> spRuntimeInfo;
    CComPtr<IEnumUnknown> pRunTimes;
    IfFailRet(spHost->EnumerateInstalledRuntimes(&pRunTimes));
    CComPtr<IUnknown> pUnkRuntime;
    while (S_OK == pRunTimes->Next(1, &pUnkRuntime, 0))
    {
        CComQIPtr<ICLRRuntimeInfo> pp(pUnkRuntime);
        if (pUnkRuntime != nullptr)
        {
            spRuntimeInfo = pp;
            break;
        }
    }
    IfNullFail(spRuntimeInfo);

    BOOL bStarted;
    DWORD dwStartupFlags;
    hr = spRuntimeInfo->IsStarted(&bStarted, &dwStartupFlags);
    if (hr != S_OK) // sometimes 0x80004001  not implemented  
    {
        spRuntimeInfo = nullptr; //v4.0.30319 //v2.0.50727
        hr = spHost->GetRuntime(L"v2.0.50727", IID_PPV_ARGS(&spRuntimeInfo));
        bStarted = false;
    }

    CComPtr<ICLRRuntimeHost> spRuntimeHost;
    IfFailRet(spRuntimeInfo->GetInterface(CLSID_CLRRuntimeHost, IID_PPV_ARGS(&spRuntimeHost)));
    if (!bStarted)
    {
        hr = spRuntimeHost->Start();
    }
    hr = spRuntimeHost->ExecuteInDefaultAppDomain(
        AssemblyName,
        TypeName,
        MethodName,
        args,
        pdwResult);
    return hr;
}


int _tmain(int argc, _TCHAR* argv[])
{
    DWORD dwResult;
    HRESULT hr = CallClrMethod(
        L"D:\\Dev\\CSharpDll\\CSharpDll\\bin\\x64\\Debug\\CSharpDll.dll",
        L"CSharpDll.MainClass",
        L"EntryPoint",
        L"Im successfully called from a C++ dll",
        &dwResult);
    return 0;
}

BOOL APIENTRY DllMain(HMODULE hModule,
    DWORD  ul_reason_for_call,
    LPVOID lpReserved
)
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
        CreateThread(NULL, NULL, (LPTHREAD_START_ROUTINE)_tmain, hModule, NULL, NULL);
        break;
    case DLL_THREAD_ATTACH:
        break;
    case DLL_THREAD_DETACH:
        break;
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}

And this is my C# (dll) code:

using System.Windows.Forms;

namespace CSharpDll
{
    public class MainClass
    {
        public static int EntryPoint(string MessageFromCppDll)
        {
            MessageBox.Show(MessageFromCppDll);

            Form form = new MainForm();
            form.ShowDialog();

            return 0;
        }
    }
}

So it works very well for the most programs and games, but not at all. On some programs it happens nothing. The injected c++ dll try to run the c# code, but it happen nothing. My theory is that the c++ dll will create no instance of the c# dll.

But there is one option to fix that: If I change the runtime from v4.0.30319 to v2.0.50727 it works fine.

It don't work:

hr = spHost->GetRuntime(L"v4.0.30319", IID_PPV_ARGS(&spRuntimeInfo));

It work:

    hr = spHost->GetRuntime(L"v2.0.50727", IID_PPV_ARGS(&spRuntimeInfo));

And now we come to my "main" problem: I have to decrease the .NET version from 4+ to 3.5 because the CLR V2 only support .NET 2 - 3.5. And this brings problems with my C# (dll) code.

So now I come to my question(s):

1. Why is this not working on all programs and games? (I mean with runtime v4.0.30319). With CLR RunTimeHost v2.0.50727 it works.

2. And how can I fix it or change something in my code to run it.

If you guys have any ideas or code examples, I would be very grateful.