Smartcrawl set_time_limit()

I'm getting the following error each time I save a page on my website:

Warning: set_time_limit(): Cannot set max execution time limit due to system policy in /wp-content/plugins/wpmu-dev-seo/includes/tools/sitemaps.php on line 143 

Warning: Cannot modify header information - headers already sent by (output started at /wp-content/plugins/wpmu-dev-seo/includes/tools/sitemaps.php:143) in /wp-includes/pluggable.php on line 1216