‘Are you sure you want to do this?’

I’ve had the last three versions of WP on my church’s website. I have NEVER been able to insert media into a post. When I try, I get “Are you sure you want to do this?” There is a “go back” link, I believe, which opens the write new post screen in the pop-up window.

HELP! This is driving me INSANE.

If this has already come up elsewhere (haven’t found that it has), can you please send me the link? Thanks!