Fatal error: Sitemap

I just upgraded to the newest version of WordPress and am having a small problem. Whenever someone posts a comment, instead of being returned to the page with the comment, they get a page that says, “Fatal error: Call to undefined function: get_home_path() in /home/content/t/e/l/tellsworth/html/wp-content/plugins/sitemap/sitemap.php on line 355.”

The comment is still posted, but I’d like to fix this. Can anyone tell me what I need to do?

Thanks for any help.