ICMP 'No response seen'

Hi
I want to know what may cause this problem, ‘No response seen to ICMP request’ Type = 8 code = 0. Let me tell you that on both computers firewall allowed icmp. But when i ping others on the same network i got reply. eg my gateway. Only when i ping PC 1 to PC 2 i got this problem or vice versa. Please help

Thanks