I seem not to be able to flag anything on this computer. Whenever I click flag, I receive the little orange box saying “Unable to load popup - please try again (click on this box to dismiss)”.
I use Firefox with NoScript (with exceptions for SO, of course), but I tried to deactivate NoScript, no change. Firefox error console shows no error. I have even tried IE with the same result (which puzzles me the most). I was able to flag at home (on a different computer).