I created a node with Boost turned on and got this warning upon saving:
Warning: array_unique(): The argument should be an array in boost_get_menu_structure() (line 806 of /hsphere/local/home/triprod/triprod.se/annat/ubercartmall/sites/all/modules/boost/boost.module).
The line comes from the function boost_get_menu_structure and looks like this:
$structure = array_unique($structure);
Maybe it's enough to make a check that $structure is an array?