It will only work with File Commander.
On kit kat, google has imposed sd card write permissions.
So only Sony stock apps can write into the partition. So you can use File Commander to cut, copy, paste, delete etc.
3rd party apps cannot modify the sd card. This has been done to increase security.
So if you are rooted, search for SD fix on play store.
If you aren't rooted, then root and fix it :P
Sent from my C6802 using XDA Premium 4 mobile app