为什么我得到“；岗位http://54.xx.xx.xx/wp-admin/admin-ajax.php500(内部服务

这是我第一次在WP上使用ajax。我正在处理一个简单的联系表格，由于某种原因，每当我点击提交时，我都会收到一个错误：

控制台上：

 POST http://54.xxx.xx.xx/wp-admin/admin-ajax.php 500 (Internal Server Error)jquery.js?ver=1.11.1:4 m.ajaxTransport.sendjquery.js?ver=1.11.1:4 m.extend.ajaxmain.js:66 (anonymous function)jquery.js?ver=1.11.1:3 m.event.dispatchjquery.js?ver=1.11.1:3 m.event.add.r.handle

关于chromes"网络"：

Remote Address:54.xx.xx.xx:80
Request URL:http://54.xx.xx.xx/wp-admin/admin-ajax.php
Request Method:POST
Status Code:500 Internal Server Error
Request Headersview source
Accept:*/*
Accept-Encoding:gzip, deflate
Accept-Language:en-US,en;q=0.8
Connection:keep-alive
Content-Length:73
Content-Type:application/x-www-form-urlencoded; charset=UTF-8
Cookie:wp-settings-1=editor%3Dtinymce%26posts_list_mode%3Dlist; wp-settings-time-1=1424359234
Host:54.xx.xx.xx
Origin:http://54.xxx.xx.xx
Referer:http://54.xxx.xx.xx/?page_id=73
User-Agent:Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.115 Safari/537.36
X-Requested-With:XMLHttpRequest
Form Dataview sourceview URL encoded
action:submit_contact_form
fullname:test
email:test@gmail.com
text:test
Response Headersview source
Access-Control-Allow-Credentials:true
Access-Control-Allow-Origin:http://54.xxx.xx.xx
Cache-Control:no-cache, must-revalidate, max-age=0
Connection:close
Content-Length:0
Content-Type:text/html; charset=UTF-8
Date:Thu, 26 Feb 2015 16:10:19 GMT
Expires:Wed, 11 Jan 1984 05:00:00 GMT
Pragma:no-cache
Server:Apache/2.4.7 (Ubuntu)
X-Content-Type-Options:nosniff
X-Frame-Options:SAMEORIGIN
X-Powered-By:PHP/5.5.9-1ubuntu4.5
X-Robots-Tag:noindex

这是我的ajax部分：

//send info to php 
    $.ajax({
        beforeSend: function() {
            if ( IsEmail(email) == false) {
                $('#aboutUnsuccess').show("slow");
                $('.form_content').hide("slow");
            }
        },
        url: document.location.protocol+'//'+document.location.host+'/wp-admin/admin-ajax.php', 
        type: "POST", 
        /*action: 'submit_contact_form',*/
        data: ({ "action": "submit_contact_form", "fullname": fullname, "email": email, "text": text }), 
        success: function (results){
            if ( IsEmail(email) == true) {
                //hide table
                $('.form_content').hide('slow', function() {
                    $('.form_content').hide( "slow" );
                  });
                //show textboxes
                $('#aboutSuccess').show("slow");
                $( "#aboutSuccess" ).append( "<iframe id='"pixel-thing'" src='"http://54.xxx.xx.xx/wp-content/themes/twentyfifteen-child/thePixel.html'" width='"1'" height='"1'"  border='"0'"></iframe>" );
            }
        }
    }); 

});

这是我的php函数：

// Contact form  Ajax 
add_action('wp_ajax_nopriv_submit_contact_form', 'submit_contact_form'); 
function submit_contact_form(){
    if(isset($_POST['email'])) {
        $email = $_POST['email'];       
        $email_to = "mail@main.com";
        $host = "ssl://smtp.gmail.com:465";
        $username = 'mainmain@mail.com';
        $password = 'pass';
        $email_subject = "You have a new email from $email via sdfsdfsd.com website";
        $message = $_POST['text']; 
        $headers = array ('From' => $email, 'To' => $email_to,'Subject' => $email_subject);
        $smtp = Mail::factory('smtp',
          array ('host' => $host,
            'auth' => true,
            'username' => $username,
            'password' => $password));
        $mail = $smtp->send($email_to, $headers, $message);
        if (PEAR::isError($mail)) {
          echo($mail->getMessage());
        } else {
          echo("Message successfully sent!'n");
        }
    }

}

错误的原因可能是什么？