我正在尝试使用jqueryValidation引擎插件验证注册表单，有些验证无法正常工作

首先，我必须告诉大家，我是php的新手。我正在尝试使用jqueryValidation引擎插件来验证注册表单。我成功地验证了一些部分，现在我被困在用户名验证部分（检查用户输入的名称是否已在数据库中，如果已在，则显示"用户名已被占用"）。当我输入用户名时，会显示"正在验证请等待"提示，我无法提交表单。我使用了bootstrap 3.3.6。

这是我的注册表格

<div class="modal fade" id="signupForm" data-backdrop="false" role="dialog">
    <div class="modal-dialog">
        <div class="modal-content Popmodal">
            <div class="modal-header">
                <button type="button" class="close Popclose" data-dismiss="modal" aria-label="">
                    <span>&times;</span>
                </button>
                <h4 class="modal-title Poptit">Sign Up</h4>
            </div>
            <div class="modal-body Popbody">
                <div id="error">
                    <!-- error will be showen here ! -->
                </div>
                <form class="form-horizontal" method="post" action="registration.php" id="reg-form">
                    <div class="form-group"><br>
                        <label class="col-md-4 col-md-offset-1">User Name :</label>
                        <div class="col-md-5">
                            <input type="text" placeholder="A name that you like to use" value = "" class="form-control input-sm popname validate[required,custom[onlyLetterNumber],maxSize[20],ajax[ajaxUserCallPhp]]" name="uname" id="uname" data-errormessage-value-missing="Username is required !" data-prompt-position="bottomLeft:5,4"><br>
                        </div>
                    </div>
                    <div class="form-group">
                        <label class="col-md-4 col-md-offset-1">Email :</label>
                        <div class="col-md-5">
                            <input type="email" placeholder="Your email address" class="form-control input-sm popname validate[required,custom[email]]" name="mail" id="mail" data-errormessage-value-missing="Email is required !"  data-errormessage-custom-error="Invalid email address !" data-prompt-position="bottomLeft:5,4"><br>
                        </div>
                    </div>
                    <div class="form-group">
                        <label class="col-md-4 col-md-offset-1">Password :</label>
                        <div class="col-md-5">
                            <input type="password" maxlength="15" placeholder="Password" class="form-control input-sm popname validate[required]" name="pass" id="pass" data-errormessage-value-missing="Password is required !"  data-prompt-position="bottomLeft:5,4"><br>
                        </div>
                    </div>
                    <div class="form-group">
                        <label class="col-md-4 col-md-offset-1">Confirm Password :</label>
                        <div class="col-md-5">
                            <input type="password" maxlength="15" placeholder="Confirm password" class="form-control input-sm popname validate[required,equals[pass]]" name="cpass" id="cpass" data-errormessage-value-missing="Confirm password is required !" data-errormessage-pattern-mismatch="Password fields do not match !" data-prompt-position="bottomLeft:5,4"><br>
                        </div>
                    </div>
                    <div class="form-group">
                        <div class="col-md-2 col-md-offset-8">
                            <button type="submit" class="btn btn-success sign" value="submit" name="signup">Sign Up</button>
                        </div>
                    </div>
                 </form>
            </div>
        </div>
    </div>
</div>  

这是js部分

  <script>
    $(document).ready(function(){
    $("#reg-form").validationEngine();
  });
  </script> //this part is on the index page with signup form
"ajaxUserCallPhp": {
                "url": "ajaxValidateFieldUser.php",
                "extraDataDynamic": ['#uname'],
                "alertTextOk": "* This username is available",
                "alertText": "* This user is already taken",
                "alertTextLoad": "* Validating, please wait"
            }

这是php代码

<?php
  $validateValue=$_REQUEST['fieldValue']; 
  $validateId=$_REQUEST['uname'];

  $validateError= "This username is already taken";
  $validateSuccess= "This username is available";
   $arrayToJs = array();
   $arrayToJs[0] = $validateId;
   require_once('dbconfig.php');
   $stmt = $db_con->query('SELECT uname FROM users WHERE uname    ='$validateValue'');
   $stmt->bindValue(':uname', $uname, PDO::PARAM_STR);
   $stmt->execute();
   $res = $stmt->fetchAll(PDO::FETCH_ASSOC);
   if ($res->fetchColumn() > 0) { 
   $arrayToJs[1] = false;
   echo json_encode($arrayToJs); // RETURN ARRAY WITH ERROR
   } else{
    $arrayToJs[1] = true;
    echo json_encode($arrayToJs); // RETURN ARRAY WITH success
   }
  ?>