"Permission denied" problem is opencart 2.3.0.2

Hi,
I've installed a quick start package of a template, which is based on 2.3.0.2. Now I'm trying to test "Magic Zoom Plus" extension over this template. I've already installed that extension. Unfortunately, when I'm clicking the "Edit" button, it is giving me "Permission denied" message. I've checked the all privileges and I'm the administrator of the site.

Why this is happening? This issue is really weird. Please experts help me to overcome this issue.

Thanks in advance.

You should download the latest Version of this Extension, it has been updated
a very short time ago, to possibly now solve your problems too. Just make sure, to
manually remove all content, left by the first Installation on the server, by comparing
the content of the old Extension with the content, to be removed first from the Server.
Good Luck !
Ernie