Android: SQLiteConstraintException: error code 19: constraint failed

I checked other examples in SO and I searched a lot, nothing is working for me. The database file is this (after suggested edit).

Error

E/Database(274): android.database.sqlite.SQLiteConstraintException: error code 19: constraint failed
E/Database(274):    at android.database.sqlite.SQLiteStatement.native_execute(Native Method)
E/Database(274):    at android.database.sqlite.SQLiteStatement.execute(SQLiteStatement.java:55)
E/Database(274):    at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1549)
E/Database(274):    at android.database.sqlite.SQLiteDatabase.insert(SQLiteDatabase.java:1410)
E/Database(274):    at com.example.nycgasstationhunter.userRegister$2.onClick(userRegister.java:51)
E/Database(274):    at android.view.View.performClick(View.java:2408)
E/Database(274):    at android.view.View$PerformClick.run(View.java:8816)
E/Database(274):    at android.os.Handler.handleCallback(Handler.java:587)
E/Database(274):    at android.os.Handler.dispatchMessage(Handler.java:92)
E/Database(274):    at android.os.Looper.loop(Looper.java:123)
E/Database(274):    at android.app.ActivityThread.main(ActivityThread.java:4627)
E/Database(274):    at java.lang.reflect.Method.invokeNative(Native Method)
E/Database(274):    at java.lang.reflect.Method.invoke(Method.java:521)
E/Database(274):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
E/Database(274):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
E/Database(274):    at dalvik.system.NativeStart.main(Native Method)

Code

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;

public class userRegister extends Activity{
//database
SQLiteDatabase db;
DBHelper dbhelper;
Context ourContext;
ContentValues cv;

 public void onCreate (Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_user_register);

//database  
 dbhelper=new DBHelper(this);
 db=dbhelper.getWritableDatabase();
 cv=new ContentValues();
//editText
final EditText userEdit=(EditText)  findViewById(R.id.userEdit);
final EditText emailEdit=(EditText) findViewById(R.id.emailEdit);
final EditText passwordEdit=(EditText)  findViewById(R.id.passwordEdit);
final EditText retypePassEdit=(EditText) findViewById(R.id.retypePassEdit);
//Register button
    Button regButton = (Button) findViewById(R.id.regButton);
      regButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
    //string
    final String userName=userEdit.getText().toString();
    final String emailAddress=emailEdit.getText().toString();
    final String password=passwordEdit.getText().toString();
    final String retypePassword=retypePassEdit.getText().toString();

         if (userName.length()!=0){
            if (emailAddress.length()!=0){
              if (password.length()!=0){
                 if (retypePassword.equals(password)){
                   //save in DB
                    cv.put(DBHelper.USER, userName);
                    cv.put(DBHelper.EMAIL,emailAddress);
                    cv.put(DBHelper.PASSWORD, retypePassword); 

                    db.insert(DBHelper.USER_TABLE, null, cv);

                    Intent intent = new Intent (userRegister.this,Profile.class);    
                     startActivity(intent);
               }
                 else 
                     Toast.makeText(userRegister.this,"Password mismatch", Toast.LENGTH_SHORT).show(); 
            }
              else 
                     Toast.makeText(userRegister.this,"Invalid password", Toast.LENGTH_SHORT).show();
        }
            else 
                 Toast.makeText(userRegister.this,"Invalid email", Toast.LENGTH_SHORT).show();
    }
         else 
             Toast.makeText(userRegister.this,"Invalid user name", Toast.LENGTH_SHORT).show();
 }
});
}
}

When I insert information and press regButton, it sends me to Profile activity. There is no information being saved in database. I don't understand the error in LogCat and how can I solve that? Why there is nothing in database? (I am using SQLite Database Browser to check data.) Thank you