The Android 4.3 Update was well required by the S4 owners as they have been facing some issues for along time now. Basically the most they got is that they can’t write Apps on the SD card while it always gives errors.
Technically it is a group issue rather Application are not permitted to write on external SD card which is again a Group ID issue as the SD card is not grouped at the right place. We know that this thing is really pathetic and is blowing your head off but if you are facing it remember others are also facing it. So this will Get an Easy Update in the 4.3 Update Soon.
While there is no permanent solution for now but we can use ES File Explorer to post files to external SD card which is very easy with the App.
You can find and download the app on Google Play for free.