内部异常通过asp.net访问php web服务

Question

访问php web服务时出现此错误

System.Web.Services.Protocols.SoapHeaderException：SOAP-ERROR：编码：对象没有＆＃39;可用_credit＆＃39;属性    在System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse（SoapClientMessage消息，WebResponse响应，流responseStream，布尔asyncCall）    在System.Web.Services.Protocols.SoapHttpClientProtocol.InvokeAsyncCallback（IAsyncResult result）

使用过的代码：

private void button1_Click(object sender, EventArgs e)
    {

        try
        {

            virtualrechargeService vr = new virtualrechargeService();
            vr.GetBalanceInfoCompleted += new GetBalanceInfoCompletedEventHandler(vr_GetBalanceInfoCompleted);
            vr.GetBalanceInfoAsync("asikcse");
        }
        catch(Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }

    }
    void vr_GetBalanceInfoCompleted(object sender,GetBalanceInfoCompletedEventArgs ev)
    {
        try
        {
            Console.WriteLine(ev.Error.ToString());
            Console.WriteLine(ev.Result.client_user_id);
            //MessageBox.Show(ev.Result.client_user_id);
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }
    }