Hi, when a user isn't logged in and goes to the private messages page, they get this error:
Fatal error: Call to undefined function redirect_to_login_url() in /home/lpnet/public_html/wp-content/themes/lptheme/pm4wp-template.php on line 16
I looked in the plugin files, and it seems like that function doesn't exist.
http://wordpress.org/extend/plugins/private-messages-for-wordpress/