DLL access from Excel 2016 32 Bit get "Anwendungfehler49" - c++

Question

I get a "Anwendungsfehler 49" calling 32Bit version of dll from 32 Bit Excel 2016. Excel64 Bit with 64 Bit version of dll works fine. The Messagebox in the dll in shown but after that in the return the error occurs. Has anybody an idea for that?
Here is my dll code:
// dllmain.cpp : Definiert den Einstiegspunkt für die DLL-Anwendung.
#include "pch.h"
#include <iostream>
BOOL APIENTRY DllMain( HMODULE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}
TEST_API long myTestFunction(LPCSTR test)
{
size_t origsize = strlen(test) + 1;
const size_t newsize = 100;
size_t convertedChars = 0;
wchar_t wcstring[newsize];
mbstowcs_s(&convertedChars, wcstring, origsize, test, _TRUNCATE);
wcscat_s(wcstring, L" (wchar_t *)");
MessageBox(NULL, L"Open the message box ", wcstring, MB_OK | MB_SYSTEMMODAL);
return (long) 42;
}
// pch.h:
#ifndef PCH_H
#define PCH_H
// Fügen Sie hier Header hinzu, die vorkompiliert werden sollen.
#include "framework.h"
#endif //PCH_H
#if defined(_MSC_VER)
#include <windows.h>
#define TEST_API extern "C" __declspec(dllexport)
#else
#define TEST_API
#endif
TEST_API long myTestFunction(LPCSTR test);
Excel vba code:
#If Win64 Then
Private Declare PtrSafe Function myTestFunction Lib "MyTestDll.dll" (ByVal parameter As String) As Long
#Else
Private Declare Function myTestFunction Lib "MyTestDll32.dll" (ByVal parameter As String) As Long
#End If
Sub Test()
Dim Result As Long
Result = myTestFunction("This is a test!")
End Sub