Nice Menus not displaying in new site (worked in old one) [#2125847]

I have previously installed Nice Menus under a Mayo theme when I had my "test" site running.
Everything worked fine for me.

Installed a new copy of Drupal into the "production" location and got Drupal to access my old "test" database for content, etc. Installed Nice Menus as a new module in Drupal. Its active and configured ok.

Now I cannot get Nice Menus to display anywhere in any theme (the preferred theme, my admin theme, etc.)
No primary menu or submenus get displayed ("main menu", with the brackets, is the menu parent, -1 is the # of menus to display). When I look at the Dashboard it tells me that the "Site Menu (Nice menu)" is "empty. However I have a number of menu options entered as content. I have even entered a new test menu option and that did not display either.

In Mayo I have set it to display in the "Sidebar first" block, in Seven theme in the "dashboard (sidebar)" block.

Makes my site look miserable/unclear with only the Mayo menu operating in the header.

Can someone make sense of this please?

Thanks, cheers

Andy