[jQuery] JQUERY .POST PROBLEM

[jQuery] JQUERY .POST PROBLEM


I am having some problems with a jquery script that I am writing. The
problem is after I receive the data from the php file jquery seems to
skip the if statement. I am logging to console and it is showing yes/
no depends on email address. I am enclosing my scripts in case someone
can help me.
<script src="javascripts/jquery-1.2.6.js" type="text/javascript"
charset="utf-8"></script>
<script src="javascripts/jquery.validate.js" type="text/javascript"
charset="utf-8"></script>
<script src="javascripts/jquery.corner.js" type="text/javascript"
charset="utf-8"></script>
<script src="javascripts/jquery.lightbox.packed.js" type="text/
javascript"></script>
$(document).ready(function(){
    $("#email").blur(function(){
        var post_string = $(this).val();
        $("#msgbox").removeClass().addClass('messagebox').text
('Checking...').fadeIn(1000);
            $.post("php/email.php",{ email_check: post_string} ,function(data){
                console.log(data); // show data value in console
                 if(data=='no') { // email not avaiable
<------------------------- Skipping this area
                     $("#msgbox").fadeTo(200,0.1,function(){
                        $(this).html('email address already exists').addClass
('messageboxerror').fadeTo(900,1)
                    });
             } else { // email avaiable
<-------------------------- Always gos here no matter what
                     $("#msgbox").fadeTo(200,0.1,function(){
                        $(this).html('email available to register').addClass
('messageboxok').fadeTo(900,1);
                    });
                 } // end if
            }); // end post
    }); // end email blur
}); // end doc ready
PHP FILE
if(isset($_POST['email_check'])) {
    $email = $_POST['email_check'];
    require_once('config.inc.php');
    require(MYSQL);
    $result = @mysql_query("SELECT * FROM members WHERE (user_email =
'$email')");
    $row_num = mysql_num_rows($result);
    if( $row_num > 0){
        // "unavailable to register";
        $valid = "no";
    }else{
        // "available to register";
        $valid = "yes";
    };
    echo $valid;
    mysql_close();
}
I have been working on this all day and can not figure out why the
data is skipping the if statement. if you have any ideals please let
me know.