Due to changed permissions in Android 4, there might be trouble when writing data to your external SD card.
Luckily, there is an easy remedy for rooted devices.
Step 1 – Set the system path as read-write
I usually use Ghost Commander to perform this task with one click, however you could also accomplish this from a terminal prompt:
> su # mount -o rw,remount,rw /system
Step 2 – Edit permissions file
Find and edit the following file:
/system/etc/permissions/platform.xml
Change the entries under WRITE_EXTERNAL_STORAGE to add the media_rw permissions.
<permission name="android.permission.WRITE_EXTERNAL_STORAGE" >
<group gid="sdcard_r" />
<group gid="sdcard_rw" />
<group gid="media_rw" />
</permission>
Step 3 – Save & Reboot
Save the file and reboot your device. The writing to your SD card should work as intended and without any troubles.
References
Some additional information can be found in the below references.
Fixing external SD card write issue on Android 4.4 KitKat
Unlock external SD Card writing for all apps in Android 4.4 KitKat
openTeq 