Only Admin can add attachment to a reply !!
I have created a forum in my website, and I found out that only Admin can add attachment to a reply.
When I changed the Forum Access settings for the Registered Group, the button is not shown on the reply post!
The same issue happens for the other groups except the Admin Group!
This is not permission issue, this is new registered user restriction and antispam feature. This question was answered yesterday. Please read this support topic: