Подключение DLL, Access violation reading location

extern "C++" __declspec (dllexport) int CALLBACK MyFunction(char *str);

#include "MyDLL.h"
#include "windows.h"
 
 int WINAPI DllMain(HINSTANCE hInstance, DWORD fdReason, PVOID pvReserved) 
{
 return TRUE;
 }
 extern "C++" __declspec (dllexport) int CALLBACK MyFunction(char *str)
 {
 MessageBox(NULL,str,"Function from DLL",MB_OK);
 return 1;
 }

 #include "windows.h"
 #include "MyDLL.h"
 
 typedef int (WINAPI *SumFunctionType)(char *);
 
 int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) 
 {
    HMODULE hLib=LoadLibrary(TEXT("MyDLL.dll"));
    SumFunctionType pfnMyFunction;
    pfnMyFunction=(SumFunctionType)GetProcAddress(hLib,"MyFunction");
    int iCode=(*pfnMyFunction)("Hello");
    FreeLibrary(hLib);
    return 0;
 }

GetProcAddress(hLib,"_MyFunction");

void fnc(int m);
void fnc(double m);
void fnc(char m);

extern "C"

HMODULE hLib=LoadLibrary(TEXT("MyDLL.dll"));
     if(hLib==NULL)
      {
       MessageBox(_T("Error load library"));
        return 0;
      } 
     SumFunctionType pfnMyFunction;
 if(!pfnMyFunction=(SumFunctionType)GetProcAddress(hLib,"MyFunction"))
      {
          MessageBox(_T("Error load func"));
        return 0;
      } 
 
     int iCode=(*pfnMyFunction)("Hello");