What causes this message?

RealVNC Server has a blocklist scheme that blocks an IP address after five unsuccessful connection attempts. This is a security feature to prevent against DOS and Brute Force attacks against your computer. This is built in to VNC Server and does not rely on operating system support.

The IP address is initially blocked for 10 seconds, but this doubles for each unsuccessful attempt thereafter.

How do I reset the timeout?

To reset the blocklist, you simply need to not attempt a connection for a short period of time (see above), or restart the RealVNC Server software/the computer running RealVNC Server.

A successful connection from an IP address also resets the blocklist timeout.

What username and password should I be using?

If you have failed to enter your connection details correctly a large number of times, it's possible they are not correct. Please ensure that you are connecting to the correct RealVNC Server, and that you are entering the correct username and/or password.

If you are unsure as to the username and password required, please see this article for some suggestions: What username and password do I enter when I'm trying to connect to RealVNC Server?

Can I configure the timeout and number of attempts?

You can configure both the timeout and threshold before the timeout applies using the BlacklistTimeout and BlacklistThreshold parameters respectively.