Android app engine backend entity upload

I am trying to follow the tutorial given at; https://cloud.google.com/developers/articles/how-to-build-mobile-app-with-app-engine-backend-tutorial

I am also modifying it for my needs along the way. I managed to follow the tutorial project but when I tried my own entity classes in the backend, I get some errors. For example;

Here is the entity class I created called User;

@Entity
public class User {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;
private String name;
private String imageType;
private Blob image;

public Key getKey() {
    return key;
}
public String getName() {
    return this.name;
}

public String getImageType() {
    return imageType;
}

public byte[] getImage() {
    if (image == null) {
        return null;
    }
    return image.getBytes();
}

public void setName(String name) {
    this.name = name;
}

public void setImageType(String imageType) {
    this.imageType = imageType;
}

public void setImage(byte[] bytes) {
    this.image = new Blob(bytes);
}
}

Then I am defining an AsyncTask as it is explained in the tutorial. I want to take a photo, capture its path in the device and upload that photo to Datastore. Here is my doInBaackground method;

@Override
protected Void doInBackground(Void... params) {
    User user = new User();
    user.setName("Burak Çopur");
    Userendpoint.Builder builder = new Userendpoint.Builder(
            AndroidHttp.newCompatibleTransport(), 
            new JacksonFactory(),
            null);

    builder = CloudEndpointUtils.updateBuilder(builder);
    Userendpoint endpoint = builder.build(); 
    try {
        endpoint.insertUser(user).execute();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return null;
}

Finally I call this after camera activity returns like following;

@Override
protected void onActivityResult(int requestCode, int resultCode, 
    Intent data) {
    // Handle activity resulting from IMAGE_CAPTURE
    if(requestCode == REQUEST_IMAGE_CAPTURE){
        new UserTask().execute(getApplicationContext());
        File myFile = new File(mCurrentPhotoPath);
        if(myFile.exists())
            myFile.delete();
    }
}

I checked some similar questions but I could not find the solution. I want to see name field stored first. Then I can move on. Here is the part of error code I am getting;

07-22 02:21:28.941: W/System.err(4852): 
  com.google.api.client.googleapis.json.GoogleJsonResponseException: 
503 Service Unavailable

And here is the problematic line of code;

endpoint.insertUser(user).execute();

I am not trying to do this in local debug server as it is explained in the tutorial. I wanted to see how it works on cloud so deployed my backend project through eclipse. My admin page says my app is running. I also set LOCAL_ANDROID_RUN to false so that it won't try to use local debug server. May problem be that I am not calling new EndpointsTask().execute(); from onCreate method as it is done in the tutorial? Some of the past questions may suggesting something like this but I can't see the reason.

Thanks for any help.