错误:注意:正在尝试获取非对象的属性

我正在从事一个需要Java和PHP技术的项目。我使用Java来实现我的业务逻辑和数据源管理，而PHP则帮助使用我使用Java提供的web服务。我的问题：当我使用web服务的响应并且结果包含多个返回集合时，程序运行良好。(http://driesmeers.mamca.be/images/successpage.png)然而，一旦结果只返回一个集体响应，我就会得到如下所示的错误。(http://driesmeers.mamca.be/images/errorpage.png)

这是我的密码。PHP

<?php
  try {
$wsdl_url = 'http://localhost:8080/Mamca/MamcaWS?WSDL';
$client = new SOAPClient($wsdl_url);
$params = array(
    'projectid' => $_SESSION['projectID'],
);
$return = $client->getAlternativeListByProjectID($params);
if (isset($return->return)) {
    foreach ($return->return as $eachItem) {
        echo "<tr align='center'>";
        echo "<td align='left' class='rowDisplay'> <a href = '#' class = 'rowNumber2'>" . $eachItem->alternativedescription . "</a></td>";
        echo "<td align='left' class='rowDisplay'>" . $eachItem->alternativeGroup . "</td>";
        echo "<td align='left' class='rowDisplay'>";
        echo ($eachItem->status === 1 ? 'Active' : 'Inactive');
        echo "</td>";
        echo "<td align='center' class='rowDisplay'><img src = '../images/icons/delete.png' longdesc = 'http://.delete' /><img src = '../images/icons/table_edit.png' width = '16' height = '16' /></td>";
        echo "</tr>";
    }
}
} catch (Exception $e) {
echo "Exception occured: " . $e;
}
?>
<tr  id="ajax_response">                                         
</tr> 

WS的响应和错误输出：

 <?xml version="1.0" encoding="UTF-8"?><S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
<SOAP-ENV:Header/>
<S:Body>
    <ns2:getAlternativeListByProjectIDResponse xmlns:ns2="http://services.mamca.be.vub/">
        <return>
            <alternativeGroup>testt</alternativeGroup>
            <alternativedescription>testtt</alternativedescription>
            <alternativeid>10670</alternativeid>
            <id>19</id>
            <projectid>12313</projectid>
            <status>1</status>
        </return>
    </ns2:getAlternativeListByProjectIDResponse>
</S:Body>
 </S:Envelope>

如何解决此错误？非常感谢。