소켓 프로그래밍 WSAAsyncSelect() 관련 질문

안녕하세요. 현재 소켓프로그래밍을 공부하고 있는데요.
다음과 같이 WSAAsyncSelect함수를 활용해서 서버-클라이언트간 통신을 하는 소스코드를 작성하였습습니다.
그런데 첨부된 사진처럼 첫번째 메세지 전송은 가능한데, 그 이후부터의 메세지는 받지를 못하네요.
소스코드내에서 윈도우 메세지를 받았을때 적절하게 소켓 함수 처리도 한 거 같은데요.
어디서 문제인가요?

// WinAsyncSelect.cpp : 응용 프로그램에 대한 진입점을 정의합니다.
//

#include "stdafx.h"
#include "WinAsyncSelect.h"

#include
using namespace std;

map SocketMap;

#define MAX_LOADSTRING 100

// 전역 변수:
HINSTANCE hInst; // 현재 인스턴스입니다.
TCHAR szTitle[MAX_LOADSTRING]; // 제목 표시줄 텍스트입니다.
TCHAR szWindowClass[MAX_LOADSTRING]; // 기본 창 클래스 이름입니다.

HWND zDialog, zChat;

void MsgBox(LPCTSTR msg)
{
MessageBox(NULL, msg, _T("WinCHAT"), MB_OK);
}

void Add_ChatMsg(LPCTSTR msg)
{
SendMessage( zChat, LB_ADDSTRING, NULL, (LPARAM) msg );

int mResult = SendMessage( zChat, LB_GETCOUNT, NULL, NULL );

SendMessage( zChat, LB_SETCURSEL, (WPARAM) mResult - 1, NULL );
}

SOCKET InitSocket(HWND hWnd)
{
SOCKET mServerSocket = socket( AF_INET, SOCK_STREAM, 0);
if(mServerSocket == INVALID_SOCKET)
{
MsgBox(_T("소켓 초기화 - 실패"));
return 0;
}

SOCKADDR_IN mAddress;
ZeroMemory(&mAddress, sizeof(mAddress));

mAddress.sin_family = AF_INET;
mAddress.sin_addr.s_addr = htonl(INADDR_ANY);
mAddress.sin_port = htons(7337);

int mResult = bind(mServerSocket, (SOCKADDR*) &mAddress, sizeof(mAddress));
if(mResult == SOCKET_ERROR)
{
MsgBox(_T("bind() - 실패"));
return 0;
}

mResult = listen(mServerSocket, SOMAXCONN);
if(mResult == SOCKET_ERROR)
{
MsgBox(_T("listen() - 실패"));
return 0;
}

mResult = WSAAsyncSelect(mServerSocket, hWnd, WM_SOCKET, FD_ACCEPT | FD_CLOSE);
if(mResult == SOCKET_ERROR)
{
MsgBox(_T("WSAAsyncSelect() - 실패"));
return 0;
}

return mServerSocket;
}

void SocketProc(HWND hDlg, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
char mBuffer[256 + 1];
SOCKETINFO* mSocketInfo;

SOCKET mClientSocket;
SOCKADDR_IN mClientAddress;
int mLength = sizeof(mClientAddress);
int mResult;

if(WSAGETSELECTERROR(lParam))
{
Add_ChatMsg( _T("WSAGETSELECTERROR() 오류") );
SocketMap.erase(wParam);
return;
}

switch(WSAGETSELECTEVENT(lParam))
{
case FD_ACCEPT:
{
mClientSocket = accept(wParam, (SOCKADDR*) &mClientAddress, &mLength);
if(mClientSocket == INVALID_SOCKET)
{
MsgBox(_T("accept() - 실패"));
break;
}

sprintf(mBuffer, "접속 완료 - %s", inet_ntoa(mClientAddress.sin_addr));
Add_ChatMsg( mBuffer );

SOCKETINFO* mSocketInfo = new SOCKETINFO;
mSocketInfo->sock = mClientSocket;
mSocketInfo->recvbytes = 0;
mSocketInfo->sendbytes = 0;
mSocketInfo->recvdelayed = FALSE;

pair mData(mClientSocket, mSocketInfo);

SocketMap.insert( SocketMap.end(), mData);

mResult = WSAAsyncSelect(mClientSocket, hDlg, WM_SOCKET, FD_READ | FD_WRITE | FD_CLOSE);
if(mResult == SOCKET_ERROR)
{
Add_ChatMsg("WSAAsyncSelect() 실패");
SocketMap.erase(mClientSocket);
}
}
break;

case FD_READ:
{
mClientSocket = wParam;
SOCKETINFO* mSocketInfo = SocketMap[mClientSocket];

if(mSocketInfo->recvbytes > 0)
{
mSocketInfo->recvdelayed = TRUE;
return;
}

mResult = recv(mClientSocket, mSocketInfo->buf, 512, 0);
if(mResult == SOCKET_ERROR)
{
Add_ChatMsg(_T("recv() - 실패"));
SocketMap.erase(mClientSocket);
return;
}

mSocketInfo->recvbytes = mResult;
mSocketInfo->buf [mResult] = '\0';

sprintf(mBuffer, "수신 된 데이터: %s ", mSocketInfo->buf);
Add_ChatMsg(mBuffer);
}
break;

case FD_WRITE:
{
mClientSocket = wParam;
SOCKETINFO* mSocketInfo = SocketMap[mClientSocket];

if(mSocketInfo->recvbytes <= mSocketInfo->sendbytes)
return;

mResult = send(mClientSocket, mSocketInfo->buf + mSocketInfo->sendbytes, mSocketInfo->recvbytes - mSocketInfo->sendbytes, 0);
if(mResult == SOCKET_ERROR)
{
Add_ChatMsg("send() - 실패");
SocketMap.erase(mClientSocket);
return;
}

mSocketInfo->sendbytes += mResult;

if(mSocketInfo->recvbytes == mSocketInfo->sendbytes)
{
mSocketInfo->recvbytes = 0;
mSocketInfo->sendbytes = 0;

if(mSocketInfo->recvdelayed)
{
mSocketInfo->recvdelayed = FALSE;
PostMessage(hDlg, WM_SOCKET, wParam, FD_READ);
}
}
}
break;

case FD_CLOSE:
SocketMap.erase(wParam);
break;
}
}

BOOL CALLBACK DlgProc(HWND hDlg, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
static SOCKET mSocket;

switch(uMsg)
{
case WM_INITDIALOG:
zDialog = hDlg;
zChat = GetDlgItem(hDlg, IDC_CHAT);

mSocket = InitSocket(hDlg);
return TRUE;

case WM_SOCKET:
SocketProc(hDlg, uMsg, wParam, lParam) ;
return TRUE;

case WM_COMMAND:
switch(LOWORD(wParam))
{
case IDOK:
EndDialog(hDlg, IDOK);
return TRUE;

case IDCANCEL:
EndDialog(hDlg, IDCANCEL);
return TRUE;
}
return FALSE;
}

return FALSE;
}

int APIENTRY _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow)
{
WSADATA mWinSock;

if(WSAStartup( MAKEWORD(2, 2), &mWinSock))
{
MsgBox(_T("윈속 초기화 - 실패"));
return 0;
}

UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);

DialogBox(hInstance, MAKEINTRESOURCE(IDD_MAIN), NULL, DlgProc);

WSACleanup();

return 0;
}