error notice in Storefront Customise/PowerPack

I run StoreFront, have now successfully updated to Woocommerce 3.0, however when I enter Customise, with or without using Powerpack the right hand side of the screen display instead of the image of the site runs a series of

Notices – Trying to get property of non object in home/i…2/public_html/wp-includes/nav-menu.php on line 727

this is repeated twice and followed by

Notices – Trying to get property of non object in home/i…2/public_html/wp-includes/nav-menu.php on line 731

these notices run the full right hand side of display.

Can someone help ?