Applica queste modifiche
<permission name="android.permission.WRITE_EXTERNAL_STORAGE" >
<group gid="sdcard_r" />
<group gid="sdcard_rw" />
<group gid="media_rw" />
</permission>
al file /system/etc/permissions/platform.xml cercando: android.permission.WRITE_EXTERNAL_STORAGE
Oppure vai qui: https://www.androidiani.com/forum/mo...d-esterna.html