VNC Server has a 'blacklisting' 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.
The IP address is initially blocked for ten seconds, but this doubles for each unsuccessful attempt thereafter.
A successful connection from an IP address resets the blacklist timeout. This is built in to VNC Server and does not rely on operating system support.
To reset the blacklist, you simply need to not attempt a connection for a short period of time, or restart the VNC Server software.
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 VNC 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 VNC Server?