Multisite Unable to Create Directory

Hi there,
I googled a lot and this is my last chance to get it.

I have a multisite installation in one of my subsites can not upload a slide. The wordpress generates the error "Error: unable to create the directory." I tried everything. I changed the permissions and tried to reinstall wordpress. But the error persists.

I use multisite BitNami AWS and do not know what I do. Could anyone help me, please?