mini panel hangs previewing or adding content

new installation Drupal 7.35, Panels 7.x-3.5, Superfish 7.x-1.9, Ubuntu 12.04, Apache. AdaptiveThemes (although also on Garland).

I've completely re-installed Drupal trying to resolve this problem.

The problem appears to only happen when I add either Superfish or Nice menus, but not for any other content including standard menus. I've looked on Superfish Issues, but can't find anything there.

I create a minipanel and add Superfish or Nice menus, but it hangs when I try to preview. Screenshot here

If I remove content from one area of the minipanel, then try to add different content, I get the same "hang" - the add content window is empty and the widget just keeps turning.

When I add Nice menus to a minipanel area, then save, then click "edit", the gear wheels in the "Content" have disappeared.

If I create a new minipanel with either Superfish or Nice, it will preview the first time, but subsequently I get an endlessly rotating widget. below the preview button.

I'm successfully using the same version of Drupal and Panels and Nice on a different server. I think I may have missed something important on this server. Any help gratefully received.