Author role cannot upload images with media modal

I have a page that allows users to create posts and also upload images for those posts. New users are given author permissions. When they are logged in, they can upload images from the admin panel when editing a post and clicking on the “Add Media” tab of the tinyMCE editor. However, when clicking on that same tab from the posting page, an error occurs – “An error occurred in the upload. Please try again later.”

If I change permissions, the media modal works from the posting page, but with increased permissions, they see all of the uploaded media for the whole site(in addition to having permissions that should not be allowed). I’m trying to be able to keep the author permissions intact in order to correctly fix this problem. Any help is greatly appreciated.

Thanks!