Wireshark : Ping using Jpcap

Hello All,

I made a basic program in java using Jpcap to ping a machine. However the problem is whenever I ping using Win 7 command prompt, it returns a ping reply. However using Jpcap, it doesn't send a reply to my ping request. However I came across a strange situation. On the other machine, which I am pinging, If I open a Wireshark console and monitor the packets, it shows a ICMP request and sends a reply then. However this is not working again if I close the wireshark !!

What is the problem here ?? Is it with some Win 7 firewall or some other issues ?

I have attached the code below :

JpcapSender sender=JpcapSender.openDevice(devices[index]);
ICMPPacket p=new ICMPPacket();
p.type=ICMPPacket.ICMP_ECHO;
p.seq=1000;
p.id=999;
p.orig_timestamp=123;
p.trans_timestamp=456;
p.recv_timestamp=789;
p.setIPv4Parameter(0,false,false,false,0,false,false,false,0,1010101,100,IPPacket.IPPROTO_ICMP, InetAddress.getByName("192.168.101.18"),InetAddress.getByName("192.168.101.4"));
p.data="data".getBytes();
EthernetPacket ether=new EthernetPacket();
ether.frametype=EthernetPacket.ETHERTYPE_IP;
ether.src_mac=new byte[]{(byte)00,(byte)26,(byte)18,(byte)00,(byte)25,(byte)65}; 

ether.dst_mac=new byte[]{(byte)90,(byte)230,(byte)186,(byte)60,(byte)205,(byte)90};
p.datalink=ether;
//for(int i=0;i<10;i++)
sender.sendPacket(p);

}