Whenever I click on one of the "Add media" buttons (add image, video, etc.), the blank window/iframe overlays itself on the screen, loads for a couple seconds (but stays blank), and I'm redirected to my blog's 404 error page.
I just installed WordPress with a standard theme and plugins (I have other working blogs with these settings). Maybe I messed something up because my blog address is at the root, but the WordPress files are in a subdirectory? To the best of my knowledge, I followed the directions to do this though.
My theme is Theseus (child theme is Thematic), and the plugins are AJAX Login, cforms II, Different Posts Per Page, Extended Comment Options, Headspace 2, Live Comment Preview, Login LockDown, NextGEN Gallery, One Click Plugin Updater, Ozh' Admin Drop Down Menu, Role Scoper, SABRE, WordPress Download Monitor, WordPress Exploit Scanner, WP-Slimbox2, and WPIDS.