Ошибка Android SDK Dialog

Я работаю над приложением для входа и регистрации.
Моя проблема заключается в том, что сообщение об ошибке показывает, есть ли ошибка или регистрация прошла успешно. Так что я не знаю, где ошибка.

КОД:

package test.test.com.test;

import android.app.AlertDialog;
import android.app.DialogFragment;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.content.Intent;
import android.widget.Toast;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.ResponseHandler;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.BasicResponseHandler;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.List;


public class Registraition extends ActionBarActivity {

Button b_login;
Button b_register;
RadioGroup gender;

HttpPost httppost;
StringBuffer buffer;
HttpResponse response;
HttpClient httpclient;
List<NameValuePair> nameValuePairs;
ProgressDialog dialog = null;

EditText first_name,last_name,email,pass,cpass;
String birth,gender_value;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_registraition);
b_login = (Button)findViewById(R.id.button_go_login);

b_login.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(Registraition.this, MainActivity.class));
setContentView(R.layout.activity_main);
}
});
b_register = (Button)findViewById(R.id.button_register);

b_register.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
dialog = ProgressDialog.show(Registraition.this, "",
"Register user...", true);
new Thread(new Runnable() {
public void run() {
register();
}
}).start();
}
});
}

void register () {
try{
first_name = (EditText)findViewById(R.id.editText_firstname);
last_name = (EditText)findViewById(R.id.editText_lastname);
pass = (EditText)findViewById(R.id.editText_password);
cpass = (EditText)findViewById(R.id.editText_cpassword);
email = (EditText)findViewById(R.id.editText_email);
birth = DatePickerFragment.date;
gender = (RadioGroup)findViewById(R.id.gender);
int id = gender.getCheckedRadioButtonId();
if (id == R.id.radioButton_female){
gender_value = "female";
} else {
gender_value = "male";
}
httpclient=new DefaultHttpClient();
httppost= new HttpPost("http://192.168.178.174/app/register.php");
nameValuePairs = new ArrayList<NameValuePair>(7);
nameValuePairs.add(new BasicNameValuePair("firstname",first_name.getText().toString().trim()));
nameValuePairs.add(new BasicNameValuePair("lastname",last_name.getText().toString().trim()));
nameValuePairs.add(new BasicNameValuePair("email",email.getText().toString().trim()));  // $Edittext_value = $_POST['Edittext_value'];
nameValuePairs.add(new BasicNameValuePair("password",pass.getText().toString().trim()));
nameValuePairs.add(new BasicNameValuePair("passwordconfirm",cpass.getText().toString().trim()));
nameValuePairs.add(new BasicNameValuePair("birth",birth.trim()));
nameValuePairs.add(new BasicNameValuePair("gender",gender_value.trim()));
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
response=httpclient.execute(httppost);
ResponseHandler<String> responseHandler = new BasicResponseHandler();
final String response = httpclient.execute(httppost, responseHandler);
System.out.println("Response : " + response);
runOnUiThread(new Runnable() {
public void run() {
dialog.dismiss();
}
});

if(response.equalsIgnoreCase("Success")){
//Here the Mistacke begins
Toast.makeText(Registraition.this,"Register Success", Toast.LENGTH_SHORT).show();
startActivity(new Intent(Registraition.this, MainActivity.class));
setContentView(R.layout.activity_main);
}else {
showAlert();
}

}catch(Exception e){
dialog.dismiss();
System.out.println("Exception : " + e.getMessage());
}
}

public void showDatePickerDialog(View v) {
DialogFragment newFragment = new DatePickerFragment();
newFragment.show(getFragmentManager(), "datePicker");
}

public void showAlert(){
Registraition.this.runOnUiThread(new Runnable() {
public void run() {
AlertDialog.Builder builder = new AlertDialog.Builder(Registraition.this);
builder.setTitle("Registraition Error.");
builder.setMessage("Error on Registraition")
.setCancelable(false)
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
}
});
AlertDialog alert = builder.create();
alert.show();
}
});
}

}