[Plugin: Contact Form 7 to Database Extension] Fatal error: Call to undefined method dbrc_wpdb::set_

What version of WP are you running? Is is pre-3.1.0?

Would you try this: Edit the plugin file CFDBQueryResultIterator.php

Find this code starting line 116

// Target charset is in wp-config.php DB_CHARSET
        if (defined('DB_CHARSET') && 'DB_CHARSET' != '') {
            global $wpdb;
            $wpdb->set_charset($con,
                               DB_CHARSET,
                               (defined('DB_COLLATE') && 'DB_COLLATE' != '') ? DB_COLLATE : null);

Replace with:

// Target charset is in wp-config.php DB_CHARSET
        if (defined('DB_CHARSET')) {
            if (DB_CHARSET != '') {
                global $wpdb;
                if (method_exists($wpdb, 'set_charset')) {
                    $collate = null;
                    if (defined('DB_COLLATE')) {
                        if (DB_COLLATE != '') {
                            $collate = DB_COLLATE;
                        }
                    }
                    $wpdb->set_charset($con, DB_CHARSET, $collate);
                }
                else {
                    $setCharset = 'SET NAMES \'' . DB_CHARSET . '\'';
                    if (defined('DB_COLLATE')) {
                        if (DB_COLLATE != '') {
                            $setCharset = $setCharset . ' COLLATE \'' . DB_COLLATE . '\'';
                        }
                    }
                    mysql_query($setCharset, $con);
                }
            }

Great. I’ll push out that change in an update so everyone gets it.