🚀 go-pugleaf

I've got a Custom Error handling function that I've used for a long time:

In the Header:
void ShowLastError(LPTSTR lpszMsgTitle);

The Code:
const DWORD dwSLEFlags = FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM;
const  WORD wSLEBuffer = MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT);

void ShowLastError(LPTSTR lpszMsgTitle)
{
  LPVOID lpErrorMessage;
  FormatMessage(dwSLEFlags, NULL, GetLastError(), wSLEBuffer,
(LPTSTR)&lpErrorMessage, 0, NULL);
  MessageBox(NULL, (LPTSTR)lpErrorMessage, lpszMsgTitle, MB_OK |
MB_ICONERROR);
  LocalFree(lpErrorMessage);
}

I'd like to change this a little. Sometimes the error is ERROR_SUCCESS or
something else that I don't really want to show the error for, so I'd like
to have the option of passing in the dwError value.

I tried changing my custom code to the following, but now I get ambiguous
call to overloaded function errors:

In the new Header:
void ShowLastError(LPTSTR lpszMsgTitle, DWORD dwErr = GetLastError());

The new Code:
const DWORD dwSLEFlags = FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM;
const  WORD wSLEBuffer = MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT);

void ShowLastError(LPTSTR lpszMsgTitle, DWORD dwErr)
{
  LPVOID lpErrorMessage;
  FormatMessage(dwSLEFlags, NULL, dwErr, wSLEBuffer,
(LPTSTR)&lpErrorMessage, 0, NULL);
  MessageBox(NULL, (LPTSTR)lpErrorMessage, lpszMsgTitle, MB_OK |
MB_ICONERROR);
  LocalFree(lpErrorMessage);
}

If I do not supply a value for dwErr in the new versions, shouldn't the code
attempt to fill this with the GetLastError default?

Why am I getting this error? What is the best way to correct my code?