Android SQLiteDatabase insert method only work once

Question

I really don't know what is happening to my code. At first, i was able to insert record to my table, then in my second try it just don't run. Please Help. I passed the username through intent which pretty works.

First

 String pass = txtpass.getText().toString();
 String repass = txtpass2.getText().toString();
 String secA = txtans.getText().toString();
 String secQ = txtQ.getSelectedItem().toString();
 Message.message(this, pass+"and"+repass);
 if(pass.equals(repass))
 {
 long id = mh.insertNewAccount(username, pass, secQ, secA);
 if(id < 0)
 Message.message(this, "Unsuccesful");
 else
 {
 Message.message(this, "You may now logged in! Enjoy your experience!");
 Intent intent = new Intent(this, MainScreen.class);
 Bundle bnd=new Bundle();
 bnd.putString("username", username); 
 intent.putExtras(bnd);
 txtpass.setText("");
 txtpass2.setText("");
 txtans.setText("");
 startActivity(intent);
 }
 }
 else
 {
 Message.message_short(this, "Password didn't match!");
 txtpass.setText("");
 txtpass2.setText("");
 }
}

Second - insertNewAccount() Function

 SQLiteDatabase db = helper.getWritableDatabase();
 ContentValues contentValues = new ContentValues();
 contentValues.put(MyHelper.USER_ID, "");
 contentValues.put(MyHelper.USER_USERNAME, name);
 contentValues.put(MyHelper.USER_PASSWORD, pass);
 contentValues.put(MyHelper.USER_SECANS, secA);
 contentValues.put(MyHelper.USER_SECQUE, secQ);
 long id = db.insert(MyHelper.TABLE_USERS, null, contentValues);
 db.close();
 return id;

• Rob: What is the schema of the table (and why do you pass "" for USER_ID)?
• Mobi: in SQLiteDatabase db = helper.getWritableDatabase(); what is helper? Try this instead.
• Rob: Would that derive from SQLiteOpenHelper ?
• Justin Morris: Rob's right.. sounds like a schema issue.. like setting USER_ID as a PRIMARY KEY :)
• akoDwin: USER_ID is actually an autoincrement primary key. I already try to remove it and i just bring it back again.