Illegal string offset 'alter'

When I run cron I get this error:

Warning: Illegal string offset 'alter' in menu_item_visibility_menu_link_alter() (line 18 of /var/www/MY_SITE/public_html/sites/all/modules/menu_item_visibility/menu_item_visibility.module).

In the modules function "menu_item_visibility_menu_link_alter" $item is serialized.
The value in line (17) $item['options']['alter'] = TRUE; can not be set because $item is a string.

Something is wrong here.