java.io.ioexception:unable to open a device:255 devices are already opened

[PreethiGowri]

I'm not able to figure out this error, i have a code which sends time to a micro-controller through ethernet, It works fine for sometime later gives a error java.io.ioexception:unable to open a device:255 devices are already opened can somebody tell me what's the reason to this error and how do we solve it.

i use netbeans 7.2 IDE with framework core java and jpcap for networking.

Below is my code

 public void sendTime(Packet pack) {
 
        try {
            InetAddress src = null;
            InetAddress dest = null;
            if (pack instanceof IPPacket) {
                IPPacket ipp = (IPPacket) pack;
                src = ipp.dst_ip;
                dest = ipp.src_ip;
            }
            System.out.println("src ip: " + src);
            System.out.println("dest ip: " + dest);
            //obtain MAC address of the default gateway  
 
            EthernetPacket etherSrc = ((EthernetPacket) pack.datalink);
            byte[] gwmac = null;
            gwmac = etherSrc.src_mac;
            System.out.println("dest mac : " + gwmac);
            //Send packet
            JpcapSender sender = JpcapSender.openDevice(devices[index]);
 
            UDPPacket sendPacket = new UDPPacket(1, 9);//UDPPacket(src_port,dest_port);              
 
            /*setIPv4Parameter(int priority, boolean delay_flag, boolean through_flag, boolean realibility_flag, int rsv_typeofservice, boolean rsv_fragmentation reservation flag, boolean dont_fragment flag, boolean more_fragment flag, int offset, int ident, int time to live, int protocol, java.net.InetAddress src, java.net.InetAddress dst) 
             Sets the IPv4 parameters */
 
            sendPacket.setIPv4Parameter(0, false, false, false, 0, false, false, false, 0, 1010101, 100, IPPacket.IPPROTO_UDP,
                    src, dest);
            // count++;
            // System.out.println("count = "+count);
            String outData = SendTime();
            sendPacket.data = outData.getBytes();
            System.out.println("string sent =" + sendPacket.data);
 
            EthernetPacket ether = new EthernetPacket(); //get ethernet packet
            ether.frametype = EthernetPacket.ETHERTYPE_IP; //set frame type as IP
            //setting src nd dest MAC address
            ether.src_mac = devices[index].mac_address;
            System.out.println("source MAC address =" + ether.src_mac);
            //ether.dst_mac=new byte[]{(byte)0,(byte)6,(byte)7,(byte)8,(byte)9,(byte)10};
            ether.dst_mac = gwmac;
            System.out.println("destination MAC address =" + gwmac);
            //set datalink frame of packet as ether
            sendPacket.datalink = ether;
            sender.sendPacket(sendPacket);
        } catch (UnknownHostException ex) {
            Logger.getLogger(func.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            JOptionPane.showMessageDialog(null, ex);
        }
 
 
    }

public static String SendTime() {
 
        int week;
        Connection con = null;
        StringBuilder outData = new StringBuilder();
        try {
            Calendar currentDate = Calendar.getInstance();
            SimpleDateFormat formatter =
                    new SimpleDateFormat("00yy:MM:dd HH:mm:ss");
            week = currentDate.get(currentDate.WEEK_OF_MONTH);
            String dateNow = formatter.format(currentDate.getTime());
            String date = dateNow.toString();
            //String dateNow = formatter.format((currentDate.getTime()).toString());
            outData.append("%");
            outData.append(date).append(":").append(week).append("$");
            outData.append("#");
            System.out.println("time sent" + outData);
            System.out.println("time sent");
        } catch (Exception e) {
        }
        return outData.toString();
 
    }