cannot add photos to post

I can’t add photos to a post using the “add to editor” button in the uploaded file browser. When pressed, the button inserts the photo into the editor and the proper tags into the HTML, however when I press either “save” or “save and continue editing” the browser is redirected to the site’s public homepage (the blog is actually located on a subdirectory.) I can write and edit posts with no problem, both the “save” and “save and continue editing” functions work fine in all cases where I’m not inserting images. This problem only happens when I insert images into the post.