I am trying to change which sign-up form is used at the bottom of my emails. I go to the sign-up form and select "Change when it's used" (see screenshot 1). I then check all boxes in the pop-up (see screenshot 2). When I click save, I receive screenshot 3: Msg: NOT FOUND. I've tried checking only one box in the pop-up, no luck. This happens in both Chrome and Firefox. Please help!