I've downloaded RealVNC v 4.1 Free Ed. and installed it on a Win2000(sp5) server to test it. Initially everything worked fine but then I started getting the error message "Too many sercurity  failures. Do you wish to attempt to reconnect to 172.16.1.20?  Yes/No". I found that it never works to answer yes, regardless of how long you wait for the security block to time-out. The only thing that does work is killing the VNC service and then restarting it.

I finally removed v4.1 and re-installed v4.0 and the problem stopped entirely.

The reason I'm posting this problem to this forum is that I am using VNC Manager v2.5.73 and I have VNC set to check for server status every 15 minutes. I'm also using VNC authentication for access. Is there a chance that VNC Manager's status checking is somehow triggering RealVNC 4.1's tighter security?

For reference, here's a reply regarding the problem when I posted a question regarding this to the RealVNC discussion group. In particular, the last paragraph suggesting non-authenticated communication between my PC and the targer server.

Bob,

"Too many security failures" indicates that the IP address from which you
are connecting has been making lots of connections to the VNC Server that
didn't end up being successfully authenticated.

This is a security feature designed to prevent dictionary attacks on
servers, by preventing machines from making large numbers of connections to
a server over a short period of time.

The message is triggered by 5 failed authentication attempts, at which point
a 10 second lockout is applied before the next attempt is permitted.  The
next failed attempt causes the timeout to be doubled.

Given that (I assume) you are seeing this message in spite of supplying
correct credentials each time you try to log in, and that once you see the
message you never again get the chance to enter a password, it sounds like
something is connecting to the server from the same IP address as your
viewer machine and is not authenticating, hence causing the failures.

VNC 4.0 was less secure in this respect, by default, hence the different
behaviour.

Cheers,

Wez @ RealVNC Ltd.

For testing purposes, I un-installed RealVNC v4.0 and re-installed v4.1 on the server having the problem. I then removed this server from VNC Manager and left everything connected overnight. In the morning, I was able to log into the server directly through RealVNC.

Now here's a strange development. I added the server  back into VNC Manager with updates still happening every 15 minutes. I have been running that for about 6 hours now and no "security failures". I plan to install RealVNC 4.1 on a couple other systems and see how they work.

Bob,
could you please send config.xml and vnc_servers.xml to support@s-code.com ? The files are located at:
%USERPROFILE%\Application Data\Smart Code\VNC\Manager

PS: I need the files from the PC, on which you able to reproduce the problem.

Bob,
I have an idea what might cause this behavior. In case if you have a server with the same IP added to a different folders, when during status update the server will be updated several times. Hence VNC Manager, will establish several connections to the VNC server within short time interval. What might cause security protection mechanism to trigger.

Let me know if that's so.