Starting with the new firmware update of Android 4.4+ (KitKat) , phones with External SD Cards do not allow 3rd Party apps to create/modify/delete files on External SD Card. This includes Samsung Galaxy Note 3, S4 and some LG phones.
Because of this problem my Backup and Restore apps cannot create backups on the External SD Card.
This has to do with the way permissions work on Android and currently there is no known workarounds unless the phone is rooted.
If your phone is rooted,
Please take a look at http://forum.xda-developers.com/showthread.php?t=2607215
For more technical information, take a look at https://source.android.com/devices/tech/storage/index.html