Activation brought my site down

I’ve been using Wordfence on a couple other sites and liked so much that I wanted it on my company’s production site. I installed but after clicking Activate I got the error that my site “isn’t working”. It was dead until I went and renamed the plugins directory. I wanted to open a support issue but found I couldn’t unless I had the Premium version which I cannot buy because I can’t use it on my production site because of the issue. I know that the site’s WP version is older (3.5.1). IS that the problem possibly? Is there a minimum version supported?