This is likely related to a known issue with some Android builds where the OS fails to return an app's internal "root" or "app data" path. According to Google, uninstalling and reinstalling the app may resolve the issue. If your device contains an SD card then please note that uninstalling the app should not wipe out your settings. However, if your device does not contain an SD card (or it is temporarily removed or unmounted when the app is run again), you will lose your app settings.
Starting with v2.2.2 the app will handle this problem more gracefully but please note that this is not a specific problem with the app but rather it is a problem with certain builds of Android itself.