Android sqlite getdatabase called recursively

I have a problem with my database. When the application starts, it should create a database with tables if they do not exist, but the application starts immediately after launch. When I close db after opening logcat, they tell me that "I want to open an already closed object", and when I do not close the database, I got an error " getReadableDatabase called recursively". I do not know what to do. Sometimes this works, but when I unistall the application and install them again errors appear.

Error without closing:

02-20 11:50:06.980: E/AndroidRuntime(15375): FATAL EXCEPTION: main
02-20 11:50:06.980: E/AndroidRuntime(15375): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.vertretungsplan2/de.vertretungsplan2.Main}: java.lang.IllegalStateException: getDatabase called recursively
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2389)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.app.ActivityThread.access$600(ActivityThread.java:153)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1269)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.os.Looper.loop(Looper.java:137)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.app.ActivityThread.main(ActivityThread.java:5289)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at java.lang.reflect.Method.invokeNative(Native Method)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at java.lang.reflect.Method.invoke(Method.java:525)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at dalvik.system.NativeStart.main(Native Method)
02-20 11:50:06.980: E/AndroidRuntime(15375): Caused by: java.lang.IllegalStateException: getDatabase called recursively
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:204)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at de.vertretungsplan2.helper.DBHandler.insertPW(DBHandler.java:89)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at de.vertretungsplan2.helper.DBHandler.onCreate(DBHandler.java:46)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:252)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at de.vertretungsplan2.Main.onCreate(Main.java:42)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.app.Activity.performCreate(Activity.java:5133)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-20 11:50:06.980: E/AndroidRuntime(15375):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2293)
02-20 11:50:06.980: E/AndroidRuntime(15375):    ... 11 more

Error closing:

02-20 11:57:47.880: E/AndroidRuntime(15853): FATAL EXCEPTION: main
02-20 11:57:47.880: E/AndroidRuntime(15853): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.vertretungsplan2/de.vertretungsplan2.Main}: java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase: /data/data/de.vertretungsplan2/databases/settings
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2389)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.app.ActivityThread.access$600(ActivityThread.java:153)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1269)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.os.Looper.loop(Looper.java:137)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.app.ActivityThread.main(ActivityThread.java:5289)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at java.lang.reflect.Method.invokeNative(Native Method)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at java.lang.reflect.Method.invoke(Method.java:525)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at dalvik.system.NativeStart.main(Native Method)
02-20 11:57:47.880: E/AndroidRuntime(15853): Caused by: java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase: /data/data/de.vertretungsplan2/databases/settings
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.database.sqlite.SQLiteClosable.acquireReference(SQLiteClosable.java:55)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.database.sqlite.SQLiteDatabase.endTransaction(SQLiteDatabase.java:520)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:263)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at de.vertretungsplan2.Main.onCreate(Main.java:42)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.app.Activity.performCreate(Activity.java:5133)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-20 11:57:47.880: E/AndroidRuntime(15853):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2293)
02-20 11:57:47.880: E/AndroidRuntime(15853):    ... 11 more

This is my DBHandler:

package de.vertretungsplan2.helper;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBHandler extends SQLiteOpenHelper {

    private static final String TAG = "DBHandler";
    //Attributes of Database
    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "settings";

    //Attributes of table "PASSWORD"
    private static final String TABLE_NAME_PW = "password";
    private static final String PASSWORD_ID ="id";
    private static final String PASSWORD_NAME = "password";

    //Attributes of table "KURS"
    private static final String TABLE_NAME_KURS = "kurs";
    private static final String KURS_ID = "id";
    private static final String KURS_NAME ="kurs";

    //Operations
    private static final String DROP_PW_TABLE = "DROP TABLE IF EXISTS " + TABLE_NAME_PW;
    private static final String DROP_KURS_TABLE = "DROP TABLE IF EXISTS " + TABLE_NAME_KURS;

    //Attributes of DBHandler 

    public DBHandler(Context context){
        super(context, DATABASE_NAME, null, DATABASE_VERSION);  
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        Log.i(TAG,"db aktion start, DBHandler-onCreate");
       /*
        if(db == null || !db.isOpen()) {
            db = getWritableDatabase();
        }*/
        createTables(db);
        insertPW("-1");
        insertKurs("-1");
        db.close();
        Log.i(TAG,"db aktion stop, DBHandler-onCreate");
    }

    private void createTables(SQLiteDatabase db){
        Log.i(TAG,"db aktion start, DBHandler-createTables");
        String CREATE_PW_TABLE = "CREATE TABLE IF NOT EXISTS  " + TABLE_NAME_PW +" (" + PASSWORD_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + PASSWORD_NAME + " TEXT);"; 
        String CREATE_KURS_TABLE = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME_KURS +" (" + KURS_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KURS_NAME + " TEXT);";
        if(db == null || !db.isOpen()) {
            db = getWritableDatabase();
        }
        db.execSQL(CREATE_PW_TABLE);
        Log.i(TAG,"db aktion start, nach PW Table erzeugen");
        db.execSQL(CREATE_KURS_TABLE);
        Log.i(TAG,"db aktion start, nach Kurs Table erzeugen");
        db.close();
        Log.i(TAG,"db aktion stop, DBHandler-createTables");
    }


    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.i(TAG,"db aktion start, DBHandler-onUpgrade");
        Log.w(TAG,"Upgrade der Datenbank von Version " + oldVersion 
                + " zu " + newVersion + "; alle Daten werden gelöscht");
        db.execSQL(DROP_PW_TABLE);
        Log.i(TAG,"db aktion start, OnUpgrade nach Drop PW Table");
        db.execSQL(DROP_KURS_TABLE);
        Log.i(TAG,"db aktion start, OnUpgrade nach Drop kurs Table");
        db.close();
        Log.i(TAG,"db aktion start, OnUpgrade nach close db");
        onCreate(db);
        Log.i(TAG,"db aktion stop, DBHandler-onUpgrade");
    }

    public void insertPW(String PW){
        Log.i(TAG,"db aktion start, DBHandler-insertPW");
        long rowId = -1;
        try{
            SQLiteDatabase db = null;
            if(db == null || !db.isOpen()) {
                db = getWritableDatabase();
            }
            ContentValues values = new ContentValues();
            values.put(PASSWORD_NAME, PW);
            rowId = db.insert(TABLE_NAME_PW, null, values);
            db.close();
        }catch (SQLiteException e){
            Log.e(TAG,"insert()",e);
        }finally{
            Log.d(TAG, "insert(): rowId=" + rowId);
            Log.i(TAG,"db aktion stop, DBHandler-insertPW");
        }
    }

    public void insertKurs(String Kurs){
        Log.i(TAG,"db aktion start, DBHandler-insertKurs");
        long rowId = -1;
        try{
            SQLiteDatabase db = null;
            if(db == null || !db.isOpen()) {
                db = getWritableDatabase();
            }
            ContentValues values = new ContentValues();
            values.put(KURS_NAME, Kurs);
            rowId = db.insert(TABLE_NAME_KURS, null, values);
            db.close();
        }catch (SQLiteException e){
            Log.e(TAG,"insert()",e);
        }finally{
            Log.d(TAG, "insert(): rowId=" + rowId);
            Log.i(TAG,"db aktion stop, DBHandler-insertKurs");
        }
    }

    public String getPW(){
        Log.i(TAG,"db aktion start, DBHandler-getPW");
        SQLiteDatabase db = null;
        if(db == null || !db.isOpen()) {
            db = getReadableDatabase();
        }
        Cursor cursor = db.query(TABLE_NAME_PW, new String[] {PASSWORD_ID, PASSWORD_NAME},null,null,null,null,null);
        for(int i=0; i<cursor.getCount();i++){
            cursor.moveToNext();
        }
        Log.i(TAG,"db aktion stop, DBHandler-getPW");
        db.close();
        return cursor.getString(1);
    }

    public String getKurs(){
        Log.i(TAG,"db aktion start, DBHandler-getKurs");
        SQLiteDatabase db = null;
        if(db == null || !db.isOpen()) {
            db = getReadableDatabase();
        }
        Cursor cursor = db.query(TABLE_NAME_KURS, new String[] {KURS_ID, KURS_NAME},null,null,null,null, null);
        for(int i=0; i<cursor.getCount();i++){
            cursor.moveToNext();
        }
        db.close();
        Log.i(TAG,"db aktion stop, DBHandler-getKurs");
        return cursor.getString(1);
    }

    public int getPWCount(){
        Log.i(TAG,"db aktion start, DBHandler-getPWCount");
        String query = "SELECT * FROM " + TABLE_NAME_PW;
        SQLiteDatabase db = null;
        if(db == null || !db.isOpen()) {
            db = getReadableDatabase();
        }
        Cursor cursor = db.rawQuery(query,null);
        Log.i(TAG,"db aktion stop, DBHandler-getPWCount");
        db.close();
        return cursor.getCount();
    }

    public int getKursCount(){
        Log.i(TAG,"db aktion start, DBHandler-getKursCount");
        String query = "SELECT * FROM " + TABLE_NAME_KURS;
        SQLiteDatabase db = null;
        if(db == null || !db.isOpen()) {
            db = getReadableDatabase();
        }
        Cursor cursor = db.rawQuery(query,null);
        Log.i(TAG,"db aktion stop, DBHandler-getKursCount");
        db.close();
        return cursor.getCount();
    }
}

I used these logs to find out where the error appears, but that doesn't help me.

Thanks for the help.