[Steven Zahm]

@ David

I see the error, but from which screen is the Media Manager being opened from? I need more details on how you are getting there…

That said…

This button is enabled (and meant) for admins only, this is the only role that has the unfiltered_html role capability by default. I have not tested scenarios where user roles other than admin can have use the Media Library. I’m guessing you enabled this capability for roles other than the admin. Is that correct? If you did, I very highly recommend that you remove that capability because it opens up the possibility for users to do some very, very bad things really easily because this also bypasses many of the security safeguards that WP has in place.