Redirect User on Login based on role WP 3 – Multi-Site

you need to populate the

current_user_can('') 

function before using it
using

  get_currentuserinfo();

so try this code:

add_action( 'admin_menu', 'fb_redirect_2' );

function fb_redirect_2(){
    get_currentuserinfo();
    if ( current_user_can('edit_posts')){
    //redirect here
    }
}