Talvez seja a manifestação do mesmo problema descrita aqui:
Solução alternativa para executar o servidor VNC no Windows Vista
The problems are caused by Windows Vista new security feature called Session 0 Isolation. Previous versions of Windows ran system services in the same login session as the locally logged-in user (Session 0). In Windows Vista, Session 0 is now reserved for these services, and all interactive logins are done in other sessions, causing VNC server unable to accept incoming remote control connection request.
e a solução proposta:
So in order to make VNC server on Windows Vista works properly, the workaround resolution (at least until the VNC developers to come out with proper fix or update to address the new security constraint in Windows Vista) is to run VNC server in user mode.
Ou tente se funcionar com o UltraVNC .
PS: aqui está o artigo do MSDN sobre Compatibilidade de aplicativos: isolamento da sessão 0 .