As of Android 4.4, "KitKat", Google has modified the default permissions for the external SD Card. Now it is accessible for writing only by a special user group of members called media_rw. Now apps cannot write to your removable sdcard. This app modifies a file to restore permissions to enable apps to write to removable storage.
The app requires root access to modify /system/etc/permissions/platform.xml. All it takes is one simple click of a button and all your apps will now be able to write to external storage again.