Non-static method should not be called statically?

Hi, I'm using a third party plugin called BP Group Suggestions and I've run into a small problem in the code. With debug mode on, it returns the error "Strict Standards: Non-static method BPGroupSuggest::get_hidden() should not be called statically in /home/buzbu/public_html/wp-content/plugins/bp-groups-suggestions/bp-suggest-functions.php on line 144" more than once, for similar lines of code.

Through google, I've learned that changing the function that this is under to say "public static function" as opposed to the regular "function" usually solves it, but doing that returns a syntax error: unexpected 'public' ... which is likely because no class is defined? There is no class in any of the code, so I'm a bit confused.

Here are the pieces of code returning the errors:

function bp_get_group_remove_suggestion_button($group = false) {
    global $groups_template;

    if (empty($group))
        $group = & $groups_template->group;

    if (!is_user_logged_in() || bp_group_is_user_banned($group))
        return false;

    //Group is already hidden from suggestions
    if (is_array(BPGroupSuggest::get_hidden())) {
        if (in_array($group->id, BPGroupSuggest::get_hidden())) {
            add_action('template_notices', 'bp_gs_ls_is_hidden_message');
            return false;
        }
    }
function bpgsls_remove_hidden_suggestion_and_cache($group_id, $user_id) {
    $hidden_from_suggestions = (array) BPGroupSuggest::get_hidden($user_id);

   //Group is  hidden from suggestions
    if (in_array($group_id, $hidden_from_suggestions)) {
        $hidden_from_suggestions = array_diff($hidden_from_suggestions, array($group_id));
        update_user_meta($user_id, 'hidden_group_suggestions', $hidden_from_suggestions);
        wp_cache_delete('get_users_groups_for_user' . $user_id);
    }
}

I know this is not a plugin of WPMU Dev's so I'm sorry if this is out of scope! It's not so much of the plugin itself but the PHP concept I can't grasp, so any help on that would be great. Thanks in advance!