Followed above link and now sorted...
This was the solution I used...
The long story short: Joomla! has now entered all backend items in the table #__menu. For some reason, there is an entry with ID 1 that is Menu_Item_Root. If this doesn't exist for some reason (some quickstarts of Joomlart for example don't have it), the API of Joomla! brings that error."
How to solve? Open your phpMyAdmin and execute the following query, by renaming #__menu with your actual prefix (i.e. "jos_menu"):
INSERT INTO `#__menu`
VALUES ( 1, '', 'Menu_Item_Root', 'root', '', '', '', '', 1, 0, 0, 0, 0, 0, '0000-00-00 00:00:00', 0, 0, '', 0, '', 0, 281, 0, '*', 0 ) ;
Thanks