Error message every time I install the Directory Plugin

As per Patrick's instructions, I added the code as instructioned and re-installed the plugin and, sorry to say, no luck.... error messages everywhere.

My website is:

http://www.localpediatricdentists.com

Fatal error: Call to undefined function get_page_template_slug() in /home/localped/public_html/wp-content/plugins/directory/core/main.php on line 148

I am ready to throw in the towel on this one.

alana
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original thread
https://premium.wpmudev.org/forums/topic/just-installed-the-directory-plugin-and-going-through-set#post-414693