I was recently working on a site for a client. We needed to build a page outside of WordPress but still use WordPress's built in functions. We followed the codex method for doing this found here ( http://codex.wordpress.org/Integrating_Wordpress_with_Your_Website )
Upon loading the page we were greeted with the following error : Fatal error: Call to a member function get() on a non-object in /web/content/wp-includes/query.php on line 27
After hours of narrowing down the problem we finally found that the issue was a conflict with the filename taxonomy.php.
The solution to this issue is to rename the file to something else then fix the include in ultimate-taxonomy-manager.php
I'd like to urge the developer to rename this file within the official repo as taxonomy.php is a reserved filename according to : http://codex.wordpress.org/Theme_Development#Template_Files_List