Windows re-installation, license is associated with different computer

I purchased Fences 2.01 in March 2013 for use on Win8. I have since re-installed Windows 8 on my computer a couple of times with Fences giving me no trouble. Today after installing Win8.1 on my PC I am presented with this message:

<< Unable to activate Fences. The license is currently associated with a different computer. >>

I have the same motherboard, GPU etc, hardware that are upgraded are: CPU, RAM, SSD.I have never removed Fences before I stopped using Windows. It's usually like this: Windows totally breaks for me forcing me to re-install everything, no chance to uninstall Fences and revoke license to free up another license.

How can I revoke license from other computers so that I can again be able to activate Fences 2.13 on my PC ?

EULA: Install, use and activate one (1) copy of the Software on up to five (5) unique personal computers simultaneously that are owned by you for your personal use.