I'm using the "Page Security by Contexture" plugin to secure my pages so that the one that the USP form is on is restricted to logged in users.
Users with Author rights can see image upload button in the editor and can upload images but right at the end of the upload process there is an error "An error occurred in the upload. Please try again later."
Users with Editor rights have no problems.
Users with either Editor and Author rights can upload images though the media uploader in WP admin.
So despite the upload dialogues appearing to be the same it seems that if uploading via USC I need to have a higher user role.
Any idea why this should be?