Ref: http://www.budbrain.it/index.cfm/2006/1/4/UltraVNC-and-Windows-XP-Lock

UltraVNC and Windows XP Lock

Finally I have resolved a problem with UltraVNC: I wasn’t able to connect to my pc from the internet. The ports on the router/firewall were open and forwarded to my local lan.
In fact the problem was really silly! UltraVNC, started in “application mode” not with windows services, doesn’t work if the computer is lock (press your keyboard’s windows key + L to understand what I mean with lock).
Every time I leave my home I lock down my pc… and that was the problem. Now with UltraVNC in service mode, even if I lock the computer, I can login into the system
把UltraVNC作为服务启动，远程连接没有问题.