mysqil_real_escape_string() error I can't fix
<p>Although the item is successfully added to the database, I'm not sure that I'm executing the mysql_real_escape_string() function correctly and, thus, getting the error. Any help is appreciated.</p>

<blockquote>
  <p>Success!</p>
  
  <p>Warning: array_map() [function.array-map]: Argument #2 should be an array in /home/site4/public_html/lab/mailing_list_dev_1-0/mailing_list_add.php on line 32</p>
  
  <p>Thanks for signing up!</p>
</blockquote>

<p>Here's the code in question...</p>

<pre><code>&lt;?php
// connects the database access information this file
include("mailing_list_include.php");

// the following code relates to mailing list signups only
if (($_POST) &amp;&amp; ($_POST["action"] == "sub")) {

if ($_POST["email"] == "") {
        header("Location: mailing_list_add.php");
        exit;
    } else {
        // connect to database
        doDB();

        // filtering out anything that isn't an email address
        if ( filter_var(($_POST["email"]), FILTER_VALIDATE_EMAIL)  == TRUE) {
            echo 'Success!';
        } else {
            echo 'Invalid Email Address';
            exit;
        }

        // check that the email is in the database
        emailChecker($_POST["email"]);

        // get number of results and do action
        if (mysqli_num_rows($check_res) &lt; 1) {
            // free result
            mysqli_free_result($check_res); 

            // cleans all input variables at once
            $email = array_map("mysqli_real_escape_string", ($_POST["email"]));

            // add record
            $add_sql =  "INSERT INTO subscribers (email)
                        VALUES('".$_POST["email"]."')";
            $add_res =  mysqli_query($mysqli, $add_sql)
                        or die(mysqli_error($mysqli));
            $display_block = "&lt;p&gt;Thanks for signing up!&lt;/p&gt;";

            // close connection to mysql
            mysqli_close($mysqli);
        } else {
            // print failure message
            $display_block = "You're email address, ".$_POST["email"].", is already subscribed.";
    }
}
}

?&gt;
&lt;html&gt;
&lt;?php echo "$display_block";?&gt;
&lt;/html&gt;
</code></pre>
