[tsu2]

Several possible issues.
Is the Server configured to "Call Back?"
Are you connecting using the VNC client or the Web Java client? - Each method uses different ports.

But, probably the more important consideration is how insecure VNC is, most documents recommend that you configure a secure tunnel to the Server before connecting (in the case of a Linux target, SSH). If you do this, then firewall issues blocking your VNC ports are moot (you only open the SSH port).

The first link in a Google search(VNC firewall ports) turns up the RealVNC FAQ. All VNC basically work the same so what you read there applies completely to your TightVNC setup.

Good Luck...