Site not available when plugin activated

Hi, the site I’m trying this on has an SSL certificate but when I activate the plugin the site becomes unavailable. When I deactivate the plugin I can access the site again. Is this likely to be a plugin conflict or something else? I tried deactivating a few plugins but had the same issue.

I only want to force https on one page and would love to be able to use this. I have a valid certificate on the site displayed at http://www.newlifeconference.co.uk

http://wordpress.org/extend/plugins/wordpress-https/