Sounds like a Firewall issue. You can temporarily switch it off to see if it makes a difference.
# service iptables stop | start
If the problem persists with the Linux Firewall off, check the Firewall on the client computer.
My firewall is disable in my db host.
I also check the firewall on client end and it is also disabled.
I also talk to my Network Administrator for adjustment in Router and Firewall to allow port 1521 to accept connection but still unsuccessful.
What seems to be the problem ?