SSHelper: SD card Permission denied
Take a look at the various ways to get around this issue as explained in the official docs.
Here're some excerpt:

One solution, not at all easy, is to take the external storage device out of the Android device, write to it elsewhere, and put it back. This is a great pain, and works only if you have access to the device and are a bit of a techie.
There's a more difficult solution that grants permanent write access in place, which I will explain here. But be warned — this is not a normal activity for end users, and without being careful you could brick your device.

The latter solution requires root access and modifying /system/etc/permissions/platform.xml to include &lt;group gid=&quot;media_rw&quot; /&gt; permission in the relevant sections as shown below:
&lt;permission name=&quot;android.permission.READ_EXTERNAL_STORAGE&quot; &gt;
    &lt;group gid=&quot;sdcard_r&quot; /&gt;
    &lt;group gid=&quot;media_rw&quot; /&gt;
&lt;/permission&gt;

&lt;permission name=&quot;android.permission.WRITE_EXTERNAL_STORAGE&quot; &gt;
    &lt;group gid=&quot;sdcard_r&quot; /&gt;
    &lt;group gid=&quot;sdcard_rw&quot; /&gt;
    &lt;group gid=&quot;media_rw&quot;/&gt;
&lt;/permission&gt;

&lt;permission name=&quot;android.permission.ACCESS_ALL_EXTERNAL_STORAGE&quot; &gt;
    &lt;group gid=&quot;sdcard_r&quot; /&gt;
    &lt;group gid=&quot;sdcard_rw&quot; /&gt;
    &lt;group gid=&quot;sdcard_all&quot; /&gt;
    &lt;group gid=&quot;media_rw&quot; /&gt;
&lt;/permission&gt;

Also note that your changes to the above file will most likely be lost when you do an OTA (Over-The-Air) update.