Reinstalled WP and fixed.
Nevermind, just needed to reload the cache. My apologies.
I even installed the PageNavi plugin and nothing comes up.
Conflict was with another plugin which was inserting something into the menu. Disabling that feature solved the conflict.
On further investigation, the problem is: if a primary menu is selected and Relationships are on, the site doesn’t work (content, menus, gone).
I can fix the problem by not specifying a primary menu for the site, but then I have no menu. Or I can turn off relationships between sites, but lose that great feature.
Any ideas on how to fix this?