i tested my app in Android 5.1 , it doesn't work.
i read the logcat i found FileNotFoundException . the file is like "/mnt/sdcard/myFolderName/myFileName.png" (pseudo names)
i don't know why, since:
1) the files are there and they can be opened by a image viewer.
2) the app runs on Android 4.2.2 and 4.4.2.