Use a different slug with PMPro Series.

my_pmpros_series_registration.php

/*
	Use a different slug with PMPro Series
	
	If another plugin/page/category is conflicting on the "series" slug/keyword,
	you can change the slug used by PMPro Series by adding this code
	to your active theme's functions.php or a custom plugin.
	
	Be sure to reset your rewrite rules by going to 
	Settings --> Permalink Settings in the WP admin dashboard
	and then saving for this change to take affect.
*/
function my_pmpros_series_labels($labels) {	
	$labels['slug'] = 'course-series';
	return $labels;
}
add_filter('pmpros_series_labels', 'my_pmpros_series_labels');
function my_pmpros_series_registration($post_type) {
	$post_type['rewrite']['slug'] = 'course-series';
	return $post_type;
}
add_filter('pmpros_series_registration', 'my_pmpros_series_registration');