致命错误:在第108行的非对象上调用成员函数http_request(）

这是代码的两部分（第108行是NoBlankFunctions.php的最后一行）：似乎一切都很好。它是带有newReposnderOAuth的$responser的声明（可以假设该类工作良好，因为该公司的许多其他客户都在使用它）。在某个时刻，代码调用addNewUser，这是NoBlankFunctions的一部分。在这个函数中有一个对responser的调用，responser是同一php文件中的另一个函数。最后，当尝试发送http请求时，它会崩溃。

include 'OAuth.php';
include 'responder_sdk.php';
include 'NoBlankFunctions.php';
$client_key = '28FB957EA00B920BE7F83A365CC7ABAF';    
$client_secret = '0B06B5A69DB0F3BCB80A716031C2DE6C';  
$user_key = '1F566B1DE821BE68B5F485F75610F610';  
$user_secret = '5D1406DACCA6B862AD4AE361823BB108';
$responder = new ResponderOAuth($client_key, $client_secret, $user_key, $user_secret);  
.  
.  
.  
addNewUser($registerFirstName, $registerLastName, $registerUserName,
                $registerPass, $registerEmail, $registerGender,
                $registerAge, $registerCountry, "Heb", $registerUserGMT);       

noBlankFunctions.php

function addNewUser($registerFirstName, $registerLastName, $registerUserName,
                $registerPass, $registerEmail, $registerGender,
                $registerAge, $registerCountry, $registerLang, $registerUserGMT)
{   
global $db;
$sql = "INSERT INTO `".$db."`.`users` (`userEmail`, `nickName`, `password`, `firstName`, `lastName`, `State`, `userGMT`, `language`, `gender`, `age`, `currentDay`, `dateForCurrentDay`, `isUserCheck`, `isUserDone`, `isUserPayed`)
        VALUES ('".$registerEmail."', '".$registerUserName."', '".$registerPass."', '".$registerFirstName."', '".$registerLastName."', '".$registerCountry."', '".$registerUserGMT."', '".$registerLang."', '".$registerGender."', '".$registerAge."', '0', '".date("Y/m/d")."', '0', '0', '0');";
$result = mysql_query($sql);
if ($registerLang == 'En')
{
    $listNum = 37742;
}
elseif($registerGender == 'Male')
{
    $listNum = 37713;
}
else
{
    $listNum = 37741;
}
responder($registerEmail, $registerFirstName, $listNum);
}
function responder($userMail, $userFirstName, $listNum)
{
    $post_data = array(
        'subscribers' => json_encode(
            array(
                array(
                    'EMAIL' => $userMail,
                    'NAME' => $userFirstName
                )
            )
        )
    );
$response = $responder->http_request('lists/'.$listNum.'/subscribers', 'post', $post_data);
}

有什么想法吗？