Automated test fails on button click

I downloaded a simple app from appium github and tried to write an automated test for it using Appium Server (version 1.3.3). Here is my code

import io.appium.java_client.AppiumDriver;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.openqa.selenium.By;
import org.openqa.selenium.remote.DesiredCapabilities;

import java.net.MalformedURLException;
import java.net.URL;
import java.util.concurrent.TimeUnit;

import static org.testng.AssertJUnit.assertEquals;

public class AppiumDemo {

    private AppiumDriver ad;

    @Before
    public void setupTest(){
        DesiredCapabilities capabilities = new DesiredCapabilities();
        capabilities.setCapability("appium-version", "1.3.3");
        capabilities.setCapability("platformName", "iOS");
        capabilities.setCapability("platformVersion", "7.1");
        capabilities.setCapability("deviceName", "iPhone 5s");
        capabilities.setCapability("app", "/Users/admin/Downloads/TestApp.app");
        try {
            ad = new AppiumDriver(new URL("http://ift.tt/1eWSHgW"), capabilities);
        } catch (MalformedURLException e) {
            e.printStackTrace();
        }

    }

    @After
    public void tearDown(){
        if(ad != null) ad.quit();
    }

    @Test
    public void simpleTest() {
        ad.findElement(By.name("IntegerA")).sendKeys("11");
        ad.findElement(By.name("IntegerB")).sendKeys("1");
        ad.findElement(By.name("ComputeSumButton")).click();
        int ans = Integer.parseInt(ad.findElement(By.name("Answer")).getText());
        assertEquals(ans, 12);
        ad.manage().timeouts().implicitlyWait(60, TimeUnit.SECONDS);
    }

}

it opens the simulator, enters 2 numbers, when when should click on the button to calculate the sum, test crashes, simulator is killed. in intellij it shows that it failed on the line I press click. and - Process finished with exit code 255. I use Yosemite , v. 10.10.1 installed on wmware. Please help me, what can be the reason of it ? thanks a lot.