内部异常通过asp.net访问php web服务

Question

I got this error when access a php web service

System.Web.Services.Protocols.SoapHeaderException: SOAP-ERROR: Encoding: object hasn't 'available_credit' property at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall) at System.Web.Services.Protocols.SoapHttpClientProtocol.InvokeAsyncCallback(IAsyncResult result)

Used code :

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());
        }
    }