SdCard is not usable with KitKat?
On my S4 Mini I configured the path as:

/storage/extSdCard/Android/data/mobi.infolife.appbackup/APP_Backup_Restore


and it works fine - device is not rooted.

Probably the first part (/storage/extSdCard) is different from device to device and maybe the path is case-sensitive.