[Plugin: Posts 2 Posts] Crashes WP on localhost

I am using PHP 5

When I try installing on MAMP (snow leopard) localhost,

I get an error that says

HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfill the request

Here is a screenshot: http://cl.ly/3G0k3P4014001s2Q3X0W
http://ww.wp.xz.cn/extend/plugins/posts-to-posts/