Warning: Unknown: open(/tmp/sess_fba8e825ba5250873cf3c1d296a74d5a, O_RDWR) faile

[toniologe]

Warning: Unknown: open(/tmp/sess_fba8e825ba5250873cf3c1d296a74d5a, O_RDWR) failed: Permission denied (13) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of [ External links are visible to forum administrators only ]_path is correct (/tmp) in Unknown on line 0

[XML-Sitemaps Support]

The issue is related to PHP configuration/permissions on your host (/tmp/ folder is defined as session storage on your server but it doesn't allow to write to it). It's not related to sitemap generator but to server config in general, but you can ignore the message as long you can open sitemap pages.