Recently we have moved our website from our own hosting to Pantheon. Since we've made the move the Views body field pop-up won't load anymore. Pop-ups for other field may or may not load. Also the Preview function in Views isn't working either. Because this may sound vague I've made a screencast display the problem. Also no errors are shown or created in the logs. I suspect it has something to do with AJAX.
This happened to me when I used the jQuery Update module with newer versions of jQuery (specifically 1.7). It causes several administrative oddities that you can get around, but the Views admin bug is pretty much crippling.
Here is a great patch that will allow you to choose a different version of jQuery for administrative pages, so for example, you can run jQuery 1.7 for the front end, but still use 1.4.4 for the administrative areas.