mmm...
"But one thing i noticed that in the same time i m able to ping all other subscibers from this particular server"
I dont think its the server...best thing is get local access to server connect to same switch and verify:
1. NIC is active
2. CUCM blocking other subnets other than its susbcribers
3. Connect to pc and ping from same switch
Follow up with your network admin, and check traceroutes