[Plugin: WP Favorite Posts] Not able to get post ID

Hi Huseyin and thanks for the plugin,
I am trying to get the post ID the user has in the cookies, but I am unable to do so. Do you happen to know what function I need to use?? I am trying wpfp_get_cookie with no success.
Hope you can help!

http://wordpress.org/extend/plugins/wp-favorite-posts/