Server Pinging Problem

Dear all,
I face some problem as below.

I have a sun fire 280r server in a network. From that server i am able to ping any system in any network. But i am facing the problem when i try to ping the server from outside netwok. Once i give ping command in the server then only i try to access. This incident becomes very frequent mean's after every half an hour i have to run the ping command in the server..

There is no harderrors in the server..Please suggest the solution of this problem..

Thank you in advance...

---------- Post updated at 11:21 PM ---------- Previous update was at 09:05 PM ----------

i am still waiting for any reply...

Check if your firewall blocks incomming ICMPs