Crazy error message in sitemap.xml

XML-Verarbeitungsfehler: “Junk” nach Dokument-Element

Adresse: http://www.gesetzderanziehung-practitioner.com/sitemap.xml
Zeile Nr. 41, Spalte 1:Warning: Unknown: open(/var/php_sessions/sess_435fa0956c1ce45a8947100758ebe9f6, O_RDWR) failed: No such file or directory (2) in Unknown on line 0
^

Anyone has an idea? Thank you and cheers Dirk

https://wordpress.org/plugins/google-sitemap-generator/