WCF服务返回502 Http代码(指定的网络名称不再可用)

我有一个控制台应用程序发送文件到我的WCF服务，但是当我试图发送大于4MB的文件时，我的服务响应502 http代码(代理错误-指定的网络名称不再可用)。这段代码对我来说没有意义，因为他接受小于4MB的文件。

WCF服务运行在Windows 2003服务器，IIS 6和配置文件如下。

<system.serviceModel>
    <behaviors>
        <serviceBehaviors>
            <behavior name="FileUploadServiceBehavior">
                <serviceMetadata httpGetEnabled="True" httpsGetEnabled="False" />
                <serviceDebug includeExceptionDetailInFaults="False" />
            </behavior>
        </serviceBehaviors>
    </behaviors>
    <bindings>
        <basicHttpBinding>
            <!-- buffer: 64KB; max size: 64MB -->
            <binding name="FileUploadServiceBinding"
                    transferMode="Streamed"
                    messageEncoding="Mtom"
                    maxReceivedMessageSize="67108864" maxBufferSize="65536"
                    closeTimeout="00:05:00" openTimeout="00:05:00"
                    receiveTimeout="00:10:00" sendTimeout="00:05:00">
                <security mode="None">
                    <transport clientCredentialType="None" />
                </security>
            </binding>
        </basicHttpBinding>
    </bindings>
    <services>
        <service behaviorConfiguration="FileUploadServiceBehavior" name="MyProject.ServiceFileTransfer.FileUploadService">
            <endpoint address="" binding="basicHttpBinding" contract="MyProject.ServiceFileTransfer.IFileUploadService"
               bindingConfiguration="FileUploadServiceBinding">
            </endpoint>
        </service>
    </services>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
</system.serviceModel>
<system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>
</system.webServer>

为什么当发送大于4mb的文件时返回502 Bad Gateway错误?