TCP "tcp_check_send" Problem

Hi
I use TCP library and my project work fine but when i receive a command from my client on PC and process data in my Embedded System it not work fine and tcp_check_send() return false!!!!
This condition repeat in both Server and Client mode. I feel when i receive an command i must send any act before response it???

void send_data (U8 socket,U8 protocol, U8 p2val, U8 command) {
  U8 *sendbuf;

  /* UDP */
  if (protocol == UDP) {
    /* Start Connection */
    sendbuf = udp_get_buf (SENDLEN);
                sendbuf[0] = DIVICE_ADDREES_H;
                sendbuf[1] = DIVICE_ADDREES_L;
                sendbuf[2] = command;
    sendbuf[3] = p2val;
    udp_send (socket, rem_add.IP, 1001, sendbuf, SENDLEN);
  }

  /* TCP */
  else if (protocol == TCP) {
    /* Start Connection */
    switch (tcp_get_state(socket)) {
      case TCP_STATE_FREE:
      case TCP_STATE_CLOSED:
        tcp_connect (socket, rem_add.IP, rem_add.PORT, 0);
        break;
      case TCP_STATE_CONNECT:
        if (tcp_check_send (socket) != __FALSE) {
          sendbuf = tcp_get_buf(SENDLEN);
          sendbuf[0] = DIVICE_ADDREES_H;
                                        sendbuf[1] = DIVICE_ADDREES_L;
                                        sendbuf[2] = command;
          sendbuf[3] = p2val;
          tcp_send (socket, sendbuf, SENDLEN);
        }
        break;
    }
  }
}