Un petit problème en C

Exception non gérée à 0x773815de dans itk_essai02.exe : Exception Microsoft C++ : UGS::Error::Severe à l'emplacement mémoire 0x0037f668..

SetEnvironmentVariable((LPCWSTR)"MaVariable", (LPCWSTR)"MaValeur");

#include <stdio.h>
#include <windows.h>

#define BUFSIZE 4096

int main(void)
{
  DWORD dwRet, dwErr;
  LPTSTR pszOldVal;

  if (!SetEnvironmentVariable("MaVariable", "MaValeur"))
  {
    printf("Error: cannot set the environment variable\n");
    exit(EXIT_FAILURE);
  }

  pszOldVal = (LPTSTR) malloc(BUFSIZE * sizeof(TCHAR));
  if (NULL == pszOldVal)
  {
    printf("Out of memory\n");
    exit(EXIT_FAILURE);
  }
  dwRet = GetEnvironmentVariable("MaVariable", pszOldVal, BUFSIZE);

  if (0 == dwRet)
  {
    dwErr = GetLastError();
    if (ERROR_ENVVAR_NOT_FOUND == dwErr)
    {
      printf("Environment variable does not exist.\n");
      exit(EXIT_FAILURE);
    }
    else if (BUFSIZE < dwRet)
    {
      pszOldVal = (LPTSTR) realloc(pszOldVal, dwRet * sizeof(TCHAR));
      if (NULL == pszOldVal)
      {
        printf("Out of memory\n");
        exit(EXIT_FAILURE);
      }
      dwRet = GetEnvironmentVariable("MaVariable", pszOldVal, dwRet);
      if (!dwRet)
      {
        printf("GetEnvironmentVariable failed (%ld)\n", GetLastError());
        exit(EXIT_FAILURE);
      }
    }
  }
  printf("found value: %s\n", pszOldVal);
  return 0;
}