UltraVNC

Well, I did some more testing, starting with verifying that it wasn't present in 1.0.2, which we were using when were an XP-only shop. Then I figured I might as well try 1.0.9.6.1 too.
Good news: It seems to be fixed in 1.0.9.6.1.
Bad news: Now I get to figure out how to upgrade way too many ...

New information, maybe:

1) Fifteen seconds may not be sufficient to trigger this issue. I have not yet had disconnections of 30 seconds or more fail to trigger this issue.
2) I am now able to reproduce this on my (VMware ESXi hosted) virtual machines, by changing the machine settings to disconnect ...

I have discovered an issue that seems to be triggered when the machine that a UltraVNC server loses its Ethernet connection for several seconds[0][1]. Once this happens, the server gets into a state where it will acknowledge connections on the TCP level, but never send its protocol version, thus ...

I believe I pinned down the remaining mystery condition: The "Video Hook Driver" checkbox was checked. Unchecking that on the server (that is, the server PC) caused the issue to go away.

Specifically, I had:
[poll]
TurboMode=0
PollUnderCursor=1
PollForeground=1
PollFullScreen=0
OnlyPollConsole=0 ...

If you are in front of the server, is the viewer correct displaying the workstation. Yes.
It appears that there is nothing wrong with the server->workstation connection.

The issue, as far as I can tell, is the interaction between the vnc viewer and the winvnc service on the server. Updates ...

Connection from server to workstation is good. I moved a monitor to the server, and it displayed the workstation screen as expected. Remote computer sees everything on the server, except the display from the workstation.

It turns out display from the workstation is not always black; it's just ...

Assuming DirectX mode is controlled by the checkbox in the Connection Options dialog labeled "Directx (experimental)", neither viewer is in DirectX mode – neither box is checked.

Do you run a viewer on the server already running winvnc to connect to another pc workstation running winvnc ?

Yes. The server is simultaneously running both the winvnc service and the vncviewer.

We are routinely seeing this under the following circumstances:

Our "machines" are run by two or more computers, both behind a router. The router forwards incoming UltraVNC requests to the server computer. If we need to get to the workstation computer, we then create a second UltraVNC connection ...

Even if I run the UltraVNC installer with /silent, check_install asks for permission to remove the "uvnc_service" service.

And then, when I click Yes, it stops the service, but it doesn't actually remove it.

What do I need to do to get a fully silent UltraVNC install?

I can find the Inno Setup scripts in the 1.0.8.2 source archive, but when I look in the same place for 1.0.9.5, they aren't there; it looks like all files in the UltraVNC folder were accidentally left out.