Error message

• Warning: Cannot modify header information - headers already sent by (output started at /var/www/vhosts/iqfmushromsberries.com/tandemus.eu/includes/bootstrap.inc:1640) in drupal_send_headers() (line 1499 of /var/www/vhosts/iqfmushromsberries.com/tandemus.eu/includes/bootstrap.inc).
• TypeError: Argument 1 passed to xmlsitemap_node_create_link() must be an instance of stdClass, bool given, called in /var/www/vhosts/iqfmushromsberries.com/tandemus.eu/sites/all/modules/xmlsitemap/xmlsitemap_node/xmlsitemap_node.module on line 28 in xmlsitemap_node_create_link() (line 194 of /var/www/vhosts/iqfmushromsberries.com/tandemus.eu/sites/all/modules/xmlsitemap/xmlsitemap_node/xmlsitemap_node.module).