can't copy Database file in android

I can't copy my database file from database path to my external storage path. I receive following any error

01-25 11:04:40.749  11131-11131/app.burhani.quickaccount E/SpannableStringBuilder﹕ SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length

New file was created in background method but copy file is not work it return false me. My Code is Below- Please hlp me about this

private class ExportDatabaseFileTask extends AsyncTask<String, Void, Boolean> {
        private final ProgressDialog dialog = new ProgressDialog(getActivity());

        // can use UI thread here
        protected void onPreExecute() {
            this.dialog.setMessage("Exporting database...");
            this.dialog.show();
        }

        // automatically done on worker thread (separate from UI thread)
        protected Boolean doInBackground(final String... args) {

            File dbFile =
                    new File(Environment.getDataDirectory()+"/data/app.burhani.quickaccount/databases/quickdata.db");

            File exportDir = new File(Environment.getExternalStorageDirectory(), "Quick Account/Backup");
            if (!exportDir.exists()) {
                exportDir.mkdirs();
            }

            File file = new File(exportDir, dbFile.getName());


            try {
                file.createNewFile();
                this.copyFile(dbFile, file);

                return true;
            } catch (IOException e) {
                Log.e("mypck", e.getMessage(), e);
                return false;
            }
        }

        // can use UI thread here
        protected void onPostExecute(final Boolean success) {
            if (this.dialog.isShowing()) {
                this.dialog.dismiss();
            }
            if (success) {
                Toast.makeText(getActivity(), "Export successful!", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(getActivity(), "Export failed", Toast.LENGTH_SHORT).show();
            }
        }

        void copyFile(File src, File dst) throws IOException {
            FileChannel inChannel = new FileInputStream(src).getChannel();
            FileChannel outChannel = new FileOutputStream(dst).getChannel();
            try {
                inChannel.transferTo(0, inChannel.size(), outChannel);
            } finally {
                if (inChannel != null)
                    inChannel.close();
                if (outChannel != null)
                    outChannel.close();
            }
        }

    }