Please provide some basic information about your OS version, such as Red Hat 6.4 x86_64 for example, and where you are connecting from. To see if the Firewall configuration on your server is the problem, you can simply disable it temporarily using "service iptables stop". If this corrects your problem, then you know it's the Firewall on your server system. Alternatively you can also tunnel VNC through SSH, which port is usually open.
My remote server OS is Red Hat 5.2 . And I am trying to connect to my remote host server (Red hat 5.2 ) through VNC which is installed on my local system Windows XP. I usually use putty to get command base access of my remote server. I have also configured SSH tunnel in putty so that i can connect to VNC and get GUI access of my server.
What action will taken if i run command given by you. Do I have to reboot my server, if yes then it is not possible.
$ service iptables stop
I think there is no issue of firewall. Because it asks me to enter password .That means ping to server is reachable on port 5903.
My /etc/sysconfig/vncservers file contains following entry
VNCSERVERS = "3:oracle"
And one line for display resolution.