AJAX error when trying to update menu settings

I am trying to create a page view, which has its own menu item in the context of a node. The view actually works, the page URL also works. However when I try to set up the menu options I get a pop up message with an error.
Here is what I do:
- Create the view, save it - OK
- Add a page display, give it an URL, save it - OK
- Click on the Menu link in the "Page settings" section and get the message provided in the attached screenshot. This also happens with the stable version 2.1 both in Firefox an IE.