TightVNC installed on windows mechine, but when trying to connect it on client side, "This server does not have a valid password enabled" error will show.
To workaround this, you may try:
1. Manually set value of key HKEY_LOCAL_MACHINE/SOFTWARE/ORL/WinVNC3/Default to "Password"
2. In windows server's physical console, you have to reinstall TightVNC without registering it as a service.
3. Reboot the machine.
4. In administration tab of server configurations you should deselect "Disable empty passwords"
and select "Enable applet params in URLs"
Then try reconnect to the server by client (TightVNC client or Browser with Java installed)
Also you can refer to "http://www.realvnc.com/pipermail/vnc-list/2002-April/030186.html" for info on this issue.