Question : Problem: Setting up screen sharing on an iMac for Windows VNC client

I am unable to access my (Intel) iMac running OS X 5.1 (Leopard) using the builtin in VNC screen sharing. I am trying to use the normal VNC 4.0 client running on a Vista PC. I don't know which port the iMac is listening on nor can I find out how to configure this. I need to know the port because of firewall issues (port forwarding).

Answer : Problem: Setting up screen sharing on an iMac for Windows VNC client

I found this suggestion elsewhere on the web with respect to the error message you are getting:

If you use RealVNC Viewer, under the Preferred Encoding option, select Hextile, and under the Colour Level option, select Full (all available colours).
If you do not use the settings listed above can cause the error you are reporting