UltraVNC

I am local administrator so I don't need to set authorizations.
Anyway I succeeded in logon on my machines.
I noticed that I have the problem I described when there is another user logged on and he left opened his session (by "change user" option). Is there a way to work around this issue?

I have used MSLogon and I get the UltraVNC window that asks me user and password. I insert it and I get Windows logon screen... here, when I insert password, I get the problem I described before...

When I try to logon remotely, I get Windows logon screen and I insert my password, but when I press "Enter" UltraVNC Windows closed. Can you help me please?