Nach Rückgabe von Barcodescanner-App: Can not perform this action after onSaveInstanceState​

public void StarteBarcodeScan(Activity pActivity){


        try {
            Intent localIntent = new Intent("com.google.zxing.client.android.SCAN");
            localIntent.setPackage("com.google.zxing.client.android");
            localIntent.putExtra("SAVE_HISTORY", false);


            startActivityForResult(pActivity, localIntent, Constants.BARCODE_SCAN_REQUESTED, null);


        } catch (Exception e) {
            e.printStackTrace();
            Logger.e(e, "BarcodeScanner-App nicht installiert?");
        }        
    }

public void onActivityResult(int requestCode, int resultCode, Intent intent) {
        if (requestCode == Constants.BARCODE_SCAN_REQUESTED) {
            if (resultCode == RESULT_OK) {
                String barcode = intent.getStringExtra("SCAN_RESULT");
                String format = intent.getStringExtra("SCAN_RESULT_FORMAT");
                if (!barcode.isEmpty()){
                    try {
                        this.setCurrentFragment(BuchungAnzeigeFragment.class);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
                // Handle successful scan
            } else if (resultCode == RESULT_CANCELED) {
                // Handle cancel
            }
        }
    }

// sets the current fragment
    private Fragment setCurrentFragment(Class pClass)
    {
        this.stopAutoSync();
        this.startAutoSync();


        Fragment fragment = null;
        Class fragmentClass = pClass;


        try {
            fragment = (Fragment) fragmentClass.newInstance();
            this.setToolbar(fragment);
        } catch (Exception e) {
            e.printStackTrace();
        }


        // Insert the fragment by replacing any existing fragment
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.flContent, fragment).addToBackStack(null).commit();
        this._Drawer.closeDrawers();
        return fragment;
    }