Android database closed exception

I'm working on a project where I'm downloading and saving data from web to sqlite database. A few minutes ago I receive a strange exception to our server from a user which is saying that the sqlite database is already closed..and I just checked the whole file where the exception happened and I'm not calling dbHelper.close(); . Here is the function where the app crashes and LogCat message :

public void insertCollectionCountries(JSONObject obj, Context context) {

    //Insert in collection_countries

    if(RPCCommunicator.isServiceRunning){

    Log.w("","JsonCollection - insertCollectionCountries");

    ContentValues valuesCountries = new ContentValues();



        try {

            collectionId = Integer.parseInt(obj.getString("collection_id"));

            dbHelper.deleteSQL("collection_countries", "collection_id=?", new String[] {Integer.toString(collectionId)});



           JSONArray arrayCountries = obj.getJSONArray("country_availability");

           for (int i=0; i<arrayCountries.length(); i++) {

                   valuesCountries.put("collection_id", collectionId);

                   String countryCode = arrayCountries.getString(i);

                   valuesCountries.put("country_code", countryCode);

                   dbHelper.executeQuery("collection_countries", valuesCountries);

           }

        } catch (JSONException e){

            e.printStackTrace();

        }

    }

}

and the error is on that line : dbHelper.executeQuery("collection_countries", valuesCountries);

here is the LogCat message :

java.lang.IllegalStateException: database /data/data/com.stampii.stampii/databases/stampii_sys_tpl.sqlite (conn# 0) already closed

    at android.database.sqlite.SQLiteDatabase.verifyDbIsOpen(SQLiteDatabase.java:2123)

    at android.database.sqlite.SQLiteDatabase.setTransactionSuccessful(SQLiteDatabase.java:734)

    at com.stampii.stampii.comm.rpc.SystemDatabaseHelper.execQuery(SystemDatabaseHelper.java:298)

    at com.stampii.stampii.comm.rpc.SystemDatabaseHelper.executeQuery(SystemDatabaseHelper.java:291)

    at com.stampii.stampii.jsonAPI.JsonCollection.insertCollectionCounries(JsonCollection.java:548)

    at com.stampii.stampii.jsonAPI.JsonCollection.executeInsert(JsonCollection.java:181)

    at com.stampii.stampii.collections.MyService.downloadCollections(MyService.java:122)

    at com.stampii.stampii.collections.MyService$2.run(MyService.java:74)

    at java.lang.Thread.run(Thread.java:1020)

and function in my dbHelperClass which I'm using to insert data :

public boolean executeQuery(String tableName,ContentValues values){

    return execQuery(tableName,values);

}



private  boolean execQuery(String tableName,ContentValues values){

    sqliteDb = instance.getWritableDatabase();

    sqliteDb.beginTransaction();

    sqliteDb.insert(tableName, null, values);

    sqliteDb.setTransactionSuccessful();

    sqliteDb.endTransaction();

    return true;

}

Any ideas which can close my sqlite database or what can cause that exception, because I've tested this code on a few emulators with different Android versions, different devices (HTC EVO 3D, Samsung Galaxy Nexus,HTC Desire, LG OPTIMUS PAD, Samsung Galaxy S2, Samsung Galaxy Note) and it's working fine.

Thanks in advance!