Unfortunately the update of Periodical yesterday still had a bug under Android 2 which caused a crash when you try to open the newly introduced preferences. Therefore there is now again a new version.
Since some users may have problems updating the app using the Google Play Store, you may need to remove the old version first. You can also download the APK on the project page or at F-Droid. Important: Do a backup using the menu command in the app before removing the old version!