class cast exception on button click android

Here is my code in this code i am trying to register the user by getting the basic details like firstname,lastname,email,password and put those details in my database on res.partner table. It works perfectly and as i have mentioned in my code i am getting an unique customer id whenever i click register button. Then i have an another method called registeruser wherein i am storing the emailid,password and the customerid that have been generated in the register method and storing those details in res.users table. here my problem is i am getting the class cast exception inside the register user method help me out please.

public Integer register(String Firstname,String Lastname,String Email,String Password){
        //log.debug("In Register...");

        XmlRpcClient client = getXmlRpcClient();
        try {

            HashMap<String, Object> fields = new HashMap<String, Object>();
            fields.put("name",Firstname );
            fields.put("display_name", Lastname);
            fields.put("email", Email);
            fields.put("password", Password);
            //log.debug("Got the customer fields, rpc call to create customer");

            List<Object> callParams = getCallParameters("res.partner", MainActivity.ActionType.CREATE);
            callParams.add(fields);
          //  Toast.makeText(getApplicationContext(), "4", Toast.LENGTH_LONG).show();
            Object result = client.execute("execute", callParams);
            //Toast.makeText(getApplicationContext(), "5", Toast.LENGTH_LONG).show();
            Integer customerId = (result != null) ? (Integer) result : null;
            Toast.makeText(getApplicationContext(),"Customer/Partner record created, Id = " +customerId, Toast.LENGTH_LONG).show();
            //log.debug("Customer/Partner record created, Id = " + customerId);

            //log.debug("About to create a user login in res_users");
              registerUser(Email, Password,customerId);

            return customerId;

        } catch (Exception e) {
           Toast.makeText(getApplicationContext(), "7"+e, Toast.LENGTH_LONG).show();
            System.out.println("Excpt" + e);
            Log.d(null, Log.getStackTraceString(new Exception()));
            e.printStackTrace();
            //throw e;
            //log.error(e.getMessage());
            //log.error(e.fillInStackTrace());
        }
        return 0;
    }
    private String registerUser(String Email, String Password, Integer customerId)  {
        XmlRpcClient client = getXmlRpcClient();
        Toast.makeText(getApplicationContext(), "reguser method", Toast.LENGTH_LONG).show();
        try {
            Toast.makeText(getApplicationContext(), "try block", Toast.LENGTH_LONG).show();
            HashMap<String, Object> fields = new HashMap<String, Object>();
            fields.put("login", Email);
            fields.put("password", Password);
            fields.put("partner_id", customerId);
            Toast.makeText(getApplicationContext(), "crsd put field", Toast.LENGTH_LONG).show();
            List<Object> callParams = getCallParameters("res.users", MainActivity.ActionType.CREATE);
            callParams.add(fields);
            Toast.makeText(getApplicationContext(), "Finished res.users", Toast.LENGTH_LONG).show();
            Object result = client.execute("execute", callParams);
            Toast.makeText(getApplicationContext(), "Client execut done", Toast.LENGTH_LONG).show();
            Integer userId = (result != null) ? (Integer) result : null;
            Toast.makeText(getApplicationContext(),"New user id = " +userId, Toast.LENGTH_LONG).show();
            //   log.debug("New user id = " + userId);

            return userId.toString();

        } catch (Exception e) {
            Toast.makeText(getApplicationContext(), "7"+e, Toast.LENGTH_LONG).show();
            System.out.println("Excpt" + e);
            Log.d(null, Log.getStackTraceString(new Exception()));
            e.printStackTrace();
            //log.error(e.getMessage());
            //log.error(e.fillInStackTrace());
            //  e.printStackTrace();
        }
        return "";
    }

This is my logcat