Vnc quits after the request for windows password

Hello,
The PC 1, 2, 3 and laptops are networked, and I use often UltraVNC on the PC 1 for ordering others to distance. In recent weeks, it does more with the PC 2.

Let me explain:
I run VNC client on the PC 1 (knowing that VNC server is still running on the PC 2), I connect to the PC 2 (192.168.0.15) I request the VNC password that I met, then it connects and I fall on the page where the list of user accounts. I opened one of the 3 (this is the same thing on 3) I type the password for the user, I slap on entry, and there VNC closes.

Details:
This is even if the PC 2 on the session is already open, Suite displayed.
I have not changed the settings in VNC since its installation on the PC 2 and it worked very well at first.
From the PC 1, I normally use the PC 3 and laptops, the concern does not come from it.
From the PC 2, I normally use the PC 3 and laptops (not tested the PC 1 because I have installed the VNC client)
System Restore is disabled

A little help would be welcome, thank you

Hello,
The problem has mysteriously disappear as it appeared :blink: On the one hand the better, but on the other, I would have liked to know why and how if the problem returns ...

Have you installed any programs lately? Specifically Compiz/Beryl/etc. Anything graphically intensive is what I'm specifically looking at.

When you connect to your desktop, check the connection info, is data still being sent and recieved?