无法分析日期时间类型

我正在字符串中使用soap客户端调用bluedart pincode master api，但在传递参数后，它会给出错误

请求参数-

$params = array(
            'lastSynchDate' => '06-04-2016',
            'Profile' =>
                array(
                    'Api_type' => 'S',
                    'LicenceKey'=>$licencekey,
                    'LoginID'=>$loginid,
                    'Version'=>'1.3'
                )
        );

响应错误-

The formatter threw an exception while trying to deserialize the message:
There was an error while trying to deserialize parameter http://tempuri.org/:lastSynchDate.
The InnerException message was 'There was an error deserializing the object of type System.DateTime.
The value '06-04-2016' cannot be parsed as the type 'DateTime'

我该如何解决此问题？