I'm re-posting this as a bug because it has not been solved and the (several) cases I've found about this issue have been abandoned for months.
I have the exact same problem (ajax menus don't work at all for admins) as Benjamin in #7 in this thread: https://community.openatrium.com/issues/node/2411
I've attached a screen grab of what happens when I try to drag a new block into the dashboard. Instead of seeing the gray box with a title while dragging, all I see is this weird little gray smudge. Then, after I drop it, it appears with the title only.....until I click "save changes" and it just disappears completely.
It's very frustrating. I can't customize dashboards except with a brand-new user account, and while that account can customize, I can't save the preset because as soon as I give that user admin permissions......the customize dashboard interface breaks.
And worse, from that point forward, that newly-created user can't customize the dashboards ever again: even after I disabled, uninstalled and deleted both the "Admin Module" and the "Administrator Menu" module (...and cleared caches repeatedly, and run cron.) I also tried updating both these modules and nothing changed.
So, I can't customize default dashboards - period! Is anybody working on this issue? I'm getting quite frustrated and desperate and I have a client breathing down my neck.
FWIW, I can customize my dashboard just fine here, on this website, using the same exact browser/computer. So it's not my computer.....it's somehow the permissions interfering with ajax?
Can anyone help?