Help – this plugin crashes my site

I really want to use this plug-in or at least something that does a similar function. I don’t want users of my site, to be able to get to the WP backend at all. However, whenever I activate this plug-in, it crashes my whole site, and nothing loads. I have to press back and then deactivate it from the plug-in list.

any solutions? thanks?

http://wordpress.org/extend/plugins/wp-user-frontend/