Error message

Recoverable fatal error: Argument 1 passed to xmlsitemap_node_create_link() must be an instance of stdClass, boolean given, called in /var/www/vhosts/wingfield.greenwich.sch.uk/httpdocs/sites/all/modules/xmlsitemap/xmlsitemap_node/xmlsitemap_node.module on line 28 and defined in xmlsitemap_node_create_link() (line 194 of /var/www/vhosts/wingfield.greenwich.sch.uk/httpdocs/sites/all/modules/xmlsitemap/xmlsitemap_node/xmlsitemap_node.module).