tcp_send failes to second time

as said - second call to tcp_send fails. Other side is pretty standard MFC app, so I don't expect problem to be there....

init_TcpNet ();

   _tcp_soc = tcp_get_socket (TCP_TYPE_SERVER, 0, 30, tcp_callback);
   if (_tcp_soc != 0) {
      /* Start listening on TCP port 900 */
      tcp_listen (_tcp_soc, 900);
   }
.... some junk here

// this is something I put as a test - fails on second go around
while(tcp_check_send(_tcp_soc) == __FALSE)
   {
    for(ix = 0; ix < 1000; ++ ix);
   }

   maxlen = tcp_max_dsize (_tcp_soc);

   sendbuf = tcp_get_buf (maxlen);
   memcpy (sendbuf, data, nLen);
   tcp_send (_tcp_soc, sendbuf, nLen);
   _wait_ack = TRUE;

calls are simple

 SendToTCP("AAAA",4);
 SendToTCP("BBBB",4);

what am I missing here?

thank you
Mike