Did you set up your firewall security when you installed Redhat?
If so, the firewall settings are preventing you from connecting.
I had the same problem.
Login as root, type setup at a command prompt, and select Firewall Config.
Set your settings to no firewall, reboot, and try again.
If that fixes your problem, you know it was your firewall settings.
If you re-enable your firewall settings, make sure to clear a path for your NFS shares.