Downgrade to Free magicspam

I have been paying for MagicSpam for about 3 yrs now and now that it's free in Plesk 12, I wanted to move to the free version. I uninstalled the paid version and Plesk won't let me install the free version. It says it's not available. I even tried renaming the Magicspam folder in /etc but still no joy.

How do I fully remove the remnants of paid MagicSpam so Plesk will let me install it.

Thanks in advance for your time and assistance!

matt Caswell