调用（SOAP_操作，信封）；这一行给出了java.io.ioException，原因是什么

我有一个错误：

java.io.ioException

当我执行这一行时

httpTransport.call(SOAP_ACTION, envelope);

原因是什么。。。。？谁能帮帮我吗

从昨天开始我就一直在尝试这个，但仍然失败

谢谢大家!

SoapObject object=new SoapObject(NAMESPACE, METHOD_NAME);
        object.addProperty("data", "123");// tis value u wil get frm web service it may change      
         envelope=new SoapSerializationEnvelope(SoapEnvelope.VER11);
         envelope.dotNet=true;
         envelope.setOutputSoapObject(object);
         try {
             HttpTransportSE htp=new HttpTransportSE(URL);
             htp.call(SOAP_ACTION,envelope);
             SoapPrimitive resultString=(SoapPrimitive) envelope.getResponse();
            String server_acknowledgement=resultString.toString();
            } 
         catch (Exception e) {
            // TODO: handle exception
             exceptionArise=true;
             e.printStackTrace();
        }