error checking if record updated

I am having trouble with this code.  If the user submits the form, it always returns that the account has been updated. 

if(isset($_POST['changeUname'])) {

    $newUname = $_POST['new_uname'];

    if($newUname != "" && $newUname != null) {

        $query = "SELECT uname, change_uname FROM members WHERE ID='$userID'";

        $result = mysql_query($query) or die(mysql_error());

        if (mysql_num_rows($result) > 0) {

            $row = mysql_fetch_array($result) or die(mysql_error());

            if($row['change_uname'] == 0) {

                mysql_query("UPDATE members SET uname = '$newUname', change_uname = '1' WHERE ID = '$ID'");

            } else {

                $changeUnameErrors[] =  "You cannot change your username.  You have already changed it.";

            }

        }

    } else {

        $changeUnameErrors[] =  "Please enter a valid username!";

    }

    if (mysql_affected_rows() > 0) {

        echo "<p><span style='color:red; font-weight:strong; font-size:12px;'>Your account has been successfully updated!</span><p>";

    }

}