If it didn't work, and your were running UltraVNC on a Windows PC, the host OS would intercept the Ctrl-Alt-Del combo, so the target OS wouldn't be able to receive it.
There's no way (AFAIK) around this which is, of course, the whole idea of being required to press it in the first place ;)
There's no way (AFAIK) around this which is, of course, the whole idea of being required to press it in the first place ;)