FD_ISSET macro fails...

Hi all,

I have a client server program. I am using both tcp and udp. The udp part is to basically tell a client that a server is running on that machine.The problem is that the third call to FD_ISSET fails(I have marked this with a comment //problem here). I would like to know why this is happening.Due to this reason none of the clients are able to contact the server. Can anybody help me out...The main loop of the server code is pasted below.

regards
balaji

int MainLoop(void)
{
      int client_len=0,       
                new_sock_des=0,
                sock_des=0,
      child_pid=0,
                retval=0,
                sock_opt;
         
        int   sockfdu; /*UDP socket*/
   
       char localhost[MAXHOSTNAME+1],
       display[50];
       struct hostent *hp;
       struct sockaddr_in   server_addr,
                client_addr;
        fd_set stReadFDs;
        fd_set stXcptFDs;
 

      if(InitSocket(localhost)!=TRUE)
          exit(1);

/* Get the host name and other info on which this server is run */
     if((hp = gethostbyname(localhost)) == NULL)
         err_sys("Socket Error:Cant get localhost info");

 /*Create a tcp socket */
    if((sock_des=socket(AF_INET,SOCK_STREAM,0))<0)
       err_sys("Socket Error:Cant create TCP Socket");

   /*Create a udp socket */
   if( (sockfdu = socket (AF_INET, SOCK_DGRAM,IPPROTO_UDP)) <0)
      err_sys("Socket Error:Cant create UDP Socket\n");  

     memset((char *) &server_addr,0,sizeof(server_addr));
     server_addr.sin_family=AF_INET;
     server_addr.sin_port= htons((unsigned short)Port_number);
     server_addr.sin_addr.s_addr = htonl (INADDR_ANY);
      
/* Tell the system to allow local addresses to be reused. */
     sock_opt = 1;
if (setsockopt(sock_des, SOL_SOCKET, SO_REUSEADDR, (void *)&sock_opt,sizeof (sock_opt)) == -1) {
         (void) close(sock_des);
         //return (-1);
 }


  /* Bind to the address and listen on tcp socket */
   if(bind(sock_des,(struct sockaddr *)&server_addr, sizeof(server_addr))<0)
       err_sys("Socket Error:TCP bind not successful,port no %d used by some other application",Port_number);

     
   listen(sock_des,Q_LEN);

   /* Bind to the address and listen on udp socket */
   if (bind(sockfdu, (struct sockaddr *) &server_addr, sizeof(server_addr)))
       err_sys("Socket Error:UDP bind not successful,port no %d used by some other application",Port_number);

      
   client_len=sizeof(client_addr);
      
   FD_ZERO(&stReadFDs);
   FD_ZERO(&stXcptFDs);
   FD_SET(sockfdu,&stReadFDs);
   FD_SET(sockfdu,&stXcptFDs);
   FD_SET(sock_des,&stReadFDs);
   FD_SET(sock_des,&stXcptFDs);
   

while(1)
{

     errno=0;
     retval=select(FD_SETSIZE,  &stReadFDs, NULL, &stXcptFDs, NULL);
         
      if(errno == EINTR)
      {
         FD_ZERO(&stReadFDs);
         FD_ZERO(&stXcptFDs);
         FD_SET(sockfdu,&stReadFDs);
         FD_SET(sockfdu,&stXcptFDs);
         FD_SET(sock_des,&stReadFDs);
         FD_SET(sock_des,&stXcptFDs);
         continue;
      }
   if(retval == -1)
   {
           perror("problem with select");
               exit(0);
   }
   else if (retval!=0)
   {
        if(FD_ISSET(sockfdu,&stXcptFDs))
         {
             err_ret("some exception occured \n");
             exit(0);
         }
        if(FD_ISSET(sock_des,&stXcptFDs))
        {
           err_ret("some other exception occured \n");
           exit(0);
         }
}

if(FD_ISSET(sock_des,&stReadFDs))//problem here....
{
 new_sock_des=accept(sock_des,(struct sockaddr *)&client_addr,(unsigned int*)&client_len);
  if(new_sock_des<0)
   {
      err_ret("Spotsd :accept not successful");
      continue;
   }
         
   CallProcessRequest(sock_des,new_sock_des,client_addr);
      
          
}
 else if(FD_ISSET(sockfdu,&stReadFDs))
         AutoDetectSendMessage(sockfdu);

  }  /* End of while */
}