Can't seem to publish the things I want

I keep on getting tis message:
Warning: set_time_limit() [function.set-time-limit]: Cannot set time limit in safe mode in /public/sites/www.mijnbuurtje.com/wp-content/plugins/wpmu-dev-seo/wds-files/wds-sitemaps/wds-sitemaps.php on line 42

Warning: Cannot modify header information - headers already sent by (output started at /public/sites/www.mijnbuurtje.com/wp-content/plugins/wpmu-dev-seo/wds-files/wds-sitemaps/wds-sitemaps.php:42) in /public/sites/www.mijnbuurtje.com/wp-includes/pluggable.php on line 881

What do I have to do to solve this?