Using 5.5.1 for the first time. Attributes are available ( including for Mega Menu which I have installed) but these do not seem to be showing on the Page Properties/Custom attributes page. All I get is a tabe with what appears to be a search box.

Anybody have any ideas what the problem might be? Screen shot attached.

Also (don't know if it helps), when I use the save button on the Custom Attributes page I get a "Message from webpage" regarding Flash - see second screenshot.

This is a vanilla - out of the box installation using "Plain Yoghurt" theme with a few small CSS changes.